refactor: use pinned golangci-lint Docker image for linting

Refactor Dockerfile to use a separate lint stage with a pinned
golangci-lint v2.11.3 Docker image instead of installing
golangci-lint via curl in the builder stage. This follows the
pattern used by sneak/pixa.

Changes:
- Dockerfile: separate lint stage using golangci/golangci-lint:v2.11.3
  (Debian-based, pinned by sha256) with COPY --from=lint dependency
- Bump Go from 1.24 to 1.26.1 (golang:1.26.1-bookworm, pinned)
- Bump golangci-lint from v1.64.8 to v2.11.3
- Migrate .golangci.yml from v1 to v2 format (same linters, format only)
- All Docker images pinned by sha256 digest
- Fix all lint issues from the v2 linter upgrade:
  - Add package comments to all packages
  - Add doc comments to all exported types, functions, and methods
  - Fix unchecked errors (errcheck)
  - Fix unused parameters (revive)
  - Fix gosec warnings (MaxBytesReader for form parsing)
  - Fix staticcheck suggestions (fmt.Fprintf instead of WriteString)
  - Rename DeliveryTask to Task to avoid stutter (delivery.Task)
  - Rename shadowed builtin 'max' parameter
- Update README.md version requirements

internal/database/webhook_db_manager.go

@@ -3,6 +3,7 @@ package database
 import (
 	"context"
 	"database/sql"
+	"errors"
 	"fmt"
 	"log/slog"
 	"os"
@@ -16,87 +17,82 @@ import (
 	"sneak.berlin/go/webhooker/internal/logger"
 )
 
-// nolint:revive // WebhookDBManagerParams is a standard fx naming convention
+// WebhookDBManagerParams holds the fx dependencies for
+// WebhookDBManager.
 type WebhookDBManagerParams struct {
 	fx.In
+
 	Config *config.Config
 	Logger *logger.Logger
 }
 
-// WebhookDBManager manages per-webhook SQLite database files for event storage.
-// Each webhook gets its own dedicated database containing Events, Deliveries,
-// and DeliveryResults. Database connections are opened lazily and cached.
+// errInvalidCachedDBType indicates a type assertion failure
+// when retrieving a cached database connection.
+var errInvalidCachedDBType = errors.New(
+	"invalid cached database type",
+)
+
+// WebhookDBManager manages per-webhook SQLite database files
+// for event storage. Each webhook gets its own dedicated
+// database containing Events, Deliveries, and DeliveryResults.
+// Database connections are opened lazily and cached.
 type WebhookDBManager struct {
 	dataDir string
 	dbs     sync.Map // map[webhookID]*gorm.DB
 	log     *slog.Logger
 }
 
-// NewWebhookDBManager creates a new WebhookDBManager and registers lifecycle hooks.
-func NewWebhookDBManager(lc fx.Lifecycle, params WebhookDBManagerParams) (*WebhookDBManager, error) {
+// NewWebhookDBManager creates a new WebhookDBManager and
+// registers lifecycle hooks.
+func NewWebhookDBManager(
+	lc fx.Lifecycle,
+	params WebhookDBManagerParams,
+) (*WebhookDBManager, error) {
 	m := &WebhookDBManager{
 		dataDir: params.Config.DataDir,
 		log:     params.Logger.Get(),
 	}
 
 	// Create data directory if it doesn't exist
-	if err := os.MkdirAll(m.dataDir, 0750); err != nil {
-		return nil, fmt.Errorf("creating data directory %s: %w", m.dataDir, err)
+	err := os.MkdirAll(m.dataDir, dataDirPerm)
+	if err != nil {
+		return nil, fmt.Errorf(
+			"creating data directory %s: %w",
+			m.dataDir,
+			err,
+		)
 	}
 
 	lc.Append(fx.Hook{
-		OnStop: func(_ context.Context) error { //nolint:revive // ctx unused but required by fx
+		OnStop: func(_ context.Context) error {
 			return m.CloseAll()
 		},
 	})
 
-	m.log.Info("webhook database manager initialized", "data_dir", m.dataDir)
+	m.log.Info(
+		"webhook database manager initialized",
+		"data_dir", m.dataDir,
+	)
+
 	return m, nil
 }
 
-// dbPath returns the filesystem path for a webhook's database file.
-func (m *WebhookDBManager) dbPath(webhookID string) string {
-	return filepath.Join(m.dataDir, fmt.Sprintf("events-%s.db", webhookID))
-}
-
-// openDB opens (or creates) a per-webhook SQLite database and runs migrations.
-func (m *WebhookDBManager) openDB(webhookID string) (*gorm.DB, error) {
-	path := m.dbPath(webhookID)
-	dbURL := fmt.Sprintf("file:%s?cache=shared&mode=rwc", path)
-
-	sqlDB, err := sql.Open("sqlite", dbURL)
-	if err != nil {
-		return nil, fmt.Errorf("opening webhook database %s: %w", webhookID, err)
-	}
-
-	db, err := gorm.Open(sqlite.Dialector{
-		Conn: sqlDB,
-	}, &gorm.Config{})
-	if err != nil {
-		sqlDB.Close()
-		return nil, fmt.Errorf("connecting to webhook database %s: %w", webhookID, err)
-	}
-
-	// Run migrations for event-tier models only
-	if err := db.AutoMigrate(&Event{}, &Delivery{}, &DeliveryResult{}); err != nil {
-		sqlDB.Close()
-		return nil, fmt.Errorf("migrating webhook database %s: %w", webhookID, err)
-	}
-
-	m.log.Info("opened per-webhook database", "webhook_id", webhookID, "path", path)
-	return db, nil
-}
-
-// GetDB returns the database connection for a webhook, creating the database
-// file lazily if it doesn't exist. This handles both new webhooks and existing
-// webhooks that were created before per-webhook databases were introduced.
-func (m *WebhookDBManager) GetDB(webhookID string) (*gorm.DB, error) {
+// GetDB returns the database connection for a webhook,
+// creating the database file lazily if it doesn't exist.
+func (m *WebhookDBManager) GetDB(
+	webhookID string,
+) (*gorm.DB, error) {
 	// Fast path: already open
 	if val, ok := m.dbs.Load(webhookID); ok {
 		cachedDB, castOK := val.(*gorm.DB)
 		if !castOK {
-			return nil, fmt.Errorf("invalid cached database type for webhook %s", webhookID)
+			return nil, fmt.Errorf(
+				"%w for webhook %s",
+				errInvalidCachedDBType,
+				webhookID,
+			)
 		}
+
 		return cachedDB, nil
 	}
 
@@ -106,44 +102,61 @@ func (m *WebhookDBManager) GetDB(webhookID string) (*gorm.DB, error) {
 		return nil, err
 	}
 
-	// Store it; if another goroutine beat us, close ours and use theirs
+	// Store it; if another goroutine beat us, close ours
 	actual, loaded := m.dbs.LoadOrStore(webhookID, db)
 	if loaded {
 		// Another goroutine created it first; close our duplicate
-		if sqlDB, closeErr := db.DB(); closeErr == nil {
-			sqlDB.Close()
+		sqlDB, closeErr := db.DB()
+		if closeErr == nil {
+			_ = sqlDB.Close()
 		}
+
 		existingDB, castOK := actual.(*gorm.DB)
 		if !castOK {
-			return nil, fmt.Errorf("invalid cached database type for webhook %s", webhookID)
+			return nil, fmt.Errorf(
+				"%w for webhook %s",
+				errInvalidCachedDBType,
+				webhookID,
+			)
 		}
+
 		return existingDB, nil
 	}
 
 	return db, nil
 }
 
-// CreateDB explicitly creates a new per-webhook database file and runs migrations.
-// This is called when a new webhook is created.
-func (m *WebhookDBManager) CreateDB(webhookID string) error {
+// CreateDB explicitly creates a new per-webhook database file
+// and runs migrations.
+func (m *WebhookDBManager) CreateDB(
+	webhookID string,
+) error {
 	_, err := m.GetDB(webhookID)
+
 	return err
 }
 
-// DBExists checks if a per-webhook database file exists on disk.
-func (m *WebhookDBManager) DBExists(webhookID string) bool {
+// DBExists checks if a per-webhook database file exists on
+// disk.
+func (m *WebhookDBManager) DBExists(
+	webhookID string,
+) bool {
 	_, err := os.Stat(m.dbPath(webhookID))
+
 	return err == nil
 }
 
-// DeleteDB closes the connection and deletes the database file for a webhook.
-// This performs a hard delete — the file is permanently removed.
-func (m *WebhookDBManager) DeleteDB(webhookID string) error {
+// DeleteDB closes the connection and deletes the database file
+// for a webhook. The file is permanently removed.
+func (m *WebhookDBManager) DeleteDB(
+	webhookID string,
+) error {
 	// Close and remove from cache
 	if val, ok := m.dbs.LoadAndDelete(webhookID); ok {
 		if gormDB, castOK := val.(*gorm.DB); castOK {
-			if sqlDB, err := gormDB.DB(); err == nil {
-				sqlDB.Close()
+			sqlDB, err := gormDB.DB()
+			if err == nil {
+				_ = sqlDB.Close()
 			}
 		}
 	}
@@ -151,12 +164,20 @@ func (m *WebhookDBManager) DeleteDB(webhookID string) error {
 	// Delete the main DB file and WAL/SHM files
 	path := m.dbPath(webhookID)
 	for _, suffix := range []string{"", "-wal", "-shm"} {
-		if err := os.Remove(path + suffix); err != nil && !os.IsNotExist(err) {
-			return fmt.Errorf("deleting webhook database file %s%s: %w", path, suffix, err)
+		err := os.Remove(path + suffix)
+		if err != nil && !os.IsNotExist(err) {
+			return fmt.Errorf(
+				"deleting webhook database file %s%s: %w",
+				path, suffix, err,
+			)
 		}
 	}
 
-	m.log.Info("deleted per-webhook database", "webhook_id", webhookID)
+	m.log.Info(
+		"deleted per-webhook database",
+		"webhook_id", webhookID,
+	)
+
 	return nil
 }
 
@@ -164,20 +185,97 @@ func (m *WebhookDBManager) DeleteDB(webhookID string) error {
 // Called during application shutdown.
 func (m *WebhookDBManager) CloseAll() error {
 	var lastErr error
-	m.dbs.Range(func(key, value interface{}) bool {
+
+	m.dbs.Range(func(key, value any) bool {
 		if gormDB, castOK := value.(*gorm.DB); castOK {
-			if sqlDB, err := gormDB.DB(); err == nil {
-				if closeErr := sqlDB.Close(); closeErr != nil {
+			sqlDB, err := gormDB.DB()
+			if err == nil {
+				closeErr := sqlDB.Close()
+				if closeErr != nil {
 					lastErr = closeErr
-					m.log.Error("failed to close webhook database",
+					m.log.Error(
+						"failed to close webhook database",
 						"webhook_id", key,
 						"error", closeErr,
 					)
 				}
 			}
 		}
+
 		m.dbs.Delete(key)
+
 		return true
 	})
+
 	return lastErr
 }
+
+// DBPath returns the filesystem path for a webhook's database
+// file.
+func (m *WebhookDBManager) DBPath(
+	webhookID string,
+) string {
+	return m.dbPath(webhookID)
+}
+
+func (m *WebhookDBManager) dbPath(
+	webhookID string,
+) string {
+	return filepath.Join(
+		m.dataDir,
+		fmt.Sprintf("events-%s.db", webhookID),
+	)
+}
+
+// openDB opens (or creates) a per-webhook SQLite database and
+// runs migrations.
+func (m *WebhookDBManager) openDB(
+	webhookID string,
+) (*gorm.DB, error) {
+	path := m.dbPath(webhookID)
+	dbURL := fmt.Sprintf(
+		"file:%s?cache=shared&mode=rwc",
+		path,
+	)
+
+	sqlDB, err := sql.Open("sqlite", dbURL)
+	if err != nil {
+		return nil, fmt.Errorf(
+			"opening webhook database %s: %w",
+			webhookID, err,
+		)
+	}
+
+	db, err := gorm.Open(sqlite.Dialector{
+		Conn: sqlDB,
+	}, &gorm.Config{})
+	if err != nil {
+		_ = sqlDB.Close()
+
+		return nil, fmt.Errorf(
+			"connecting to webhook database %s: %w",
+			webhookID, err,
+		)
+	}
+
+	// Run migrations for event-tier models only
+	err = db.AutoMigrate(
+		&Event{}, &Delivery{}, &DeliveryResult{},
+	)
+	if err != nil {
+		_ = sqlDB.Close()
+
+		return nil, fmt.Errorf(
+			"migrating webhook database %s: %w",
+			webhookID, err,
+		)
+	}
+
+	m.log.Info(
+		"opened per-webhook database",
+		"webhook_id", webhookID,
+		"path", path,
+	)
+
+	return db, nil
+}