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/database_test.go

@@ -1,4 +1,4 @@
-package database
+package database_test
 
 import (
 	"context"
@@ -6,37 +6,37 @@ import (
 
 	"go.uber.org/fx/fxtest"
 	"sneak.berlin/go/webhooker/internal/config"
+	"sneak.berlin/go/webhooker/internal/database"
 	"sneak.berlin/go/webhooker/internal/globals"
 	"sneak.berlin/go/webhooker/internal/logger"
 )
 
-func TestDatabaseConnection(t *testing.T) {
-	// Set up test dependencies
+func setupTestDB(
+	t *testing.T,
+) (*database.Database, *fxtest.Lifecycle) {
+	t.Helper()
+
 	lc := fxtest.NewLifecycle(t)
 
-	// Create globals
-	globals.Appname = "webhooker-test"
-	globals.Version = "test"
-
-	g, err := globals.New(lc)
-	if err != nil {
-		t.Fatalf("Failed to create globals: %v", err)
+	g := &globals.Globals{
+		Appname: "webhooker-test",
+		Version: "test",
 	}
 
-	// Create logger
-	l, err := logger.New(lc, logger.LoggerParams{Globals: g})
+	l, err := logger.New(
+		lc,
+		logger.LoggerParams{Globals: g},
+	)
 	if err != nil {
 		t.Fatalf("Failed to create logger: %v", err)
 	}
 
-	// Create config with DataDir pointing to a temp directory
 	c := &config.Config{
 		DataDir:     t.TempDir(),
 		Environment: "dev",
 	}
 
-	// Create database
-	db, err := New(lc, DatabaseParams{
+	db, err := database.New(lc, database.DatabaseParams{
 		Config: c,
 		Logger: l,
 	})
@@ -44,31 +44,45 @@ func TestDatabaseConnection(t *testing.T) {
 		t.Fatalf("Failed to create database: %v", err)
 	}
 
-	// Start lifecycle (this will trigger the connection)
+	return db, lc
+}
+
+func TestDatabaseConnection(t *testing.T) {
+	t.Parallel()
+
+	db, lc := setupTestDB(t)
 	ctx := context.Background()
-	err = lc.Start(ctx)
+
+	err := lc.Start(ctx)
 	if err != nil {
 		t.Fatalf("Failed to connect to database: %v", err)
 	}
+
 	defer func() {
-		if stopErr := lc.Stop(ctx); stopErr != nil {
-			t.Errorf("Failed to stop lifecycle: %v", stopErr)
+		stopErr := lc.Stop(ctx)
+		if stopErr != nil {
+			t.Errorf(
+				"Failed to stop lifecycle: %v",
+				stopErr,
+			)
 		}
 	}()
 
-	// Verify we can get the DB instance
 	if db.DB() == nil {
 		t.Error("Expected non-nil database connection")
 	}
 
-	// Test that we can perform a simple query
 	var result int
+
 	err = db.DB().Raw("SELECT 1").Scan(&result).Error
 	if err != nil {
 		t.Fatalf("Failed to execute test query: %v", err)
 	}
 
 	if result != 1 {
-		t.Errorf("Expected query result to be 1, got %d", result)
+		t.Errorf(
+			"Expected query result to be 1, got %d",
+			result,
+		)
 	}
 }