Update golangci-lint to v2.12.2 with canonical config (#86)

Bumps golangci-lint from v2.11.3 to v2.12.2 and adopts the canonical lint config.

## Version pins

- `Dockerfile`: `golangci/golangci-lint:v2.12.2` Debian image, pinned by digest, dated `2026-08-07`
- `script/bootstrap`: `GOLANGCI_LINT_VERSION=2.12.2` with updated sha256 pins for the `linux-amd64` and `linux-arm64` release archives

## Config

`.golangci.yml` replaced with the canonical config. The previous file kept `lll`/`funlen`/`cyclop`/`dupl` settings under the top-level `linters-settings` key, which the v2 schema ignores; the canonical config nests them under `linters.settings`, so those thresholds now actually apply. The unsupported `issues.exclude-use-default` key was dropped.

## Lint fixes (32 findings)

- `lll` (7): wrapped or shortened over-length lines (struct tag comments moved above fields, test logger construction split, `session.NewForTest` signature wrapped, shortened a `#nosec` comment)
- `goconst` (17): replaced repeated `"POST"`/`"PUT"` literals with `http.MethodPost`/`http.MethodPut`, added shared test constants for `webhooker-test`/`test`/`application/json`, and added `tmplKeyError`/`tmplKeyWebhook` constants for template data keys in `internal/handlers`
- `dupl` (8): merged `buildHTTPTargetConfig` and `buildSlackTargetConfig` into a parameterized `buildURLTargetConfig`; removed the duplicate `iWebhookDB` test helper in favor of `testWebhookDB`; extracted shared helpers in middleware and session tests

No `//nolint` directives were added and behavior is unchanged. `make check` (fmt-check, tests, lint) passes.

Note: golangci-lint v2.12 deprecates the `gomodguard` linter in favor of `gomodguard_v2`; the canonical config change for that is left for a future coordinated update.
Co-authored-by: sneak <sneak@sneak.berlin>
Reviewed-on: #86
Co-authored-by: clawbot <clawbot@noreply.example.org>
Co-committed-by: clawbot <clawbot@noreply.example.org>

internal/database/webhook_db_manager_test.go

@@ -2,6 +2,7 @@ package database_test
 
 import (
 	"context"
+	"net/http"
 	"os"
 	"path/filepath"
 	"testing"
@@ -25,8 +26,8 @@ func setupTestWebhookDBManager(
 	lc := fxtest.NewLifecycle(t)
 
 	g := &globals.Globals{
-		Appname: "webhooker-test",
-		Version: "test",
+		Appname: testAppname,
+		Version: testVersion,
 	}
 
 	l, err := logger.New(
@@ -83,10 +84,10 @@ func TestWebhookDBManager_CreateAndGetDB(t *testing.T) {
 	event := &database.Event{
 		WebhookID:    webhookID,
 		EntrypointID: uuid.New().String(),
-		Method:       "POST",
+		Method:       http.MethodPost,
 		Headers:      `{"Content-Type":["application/json"]}`,
 		Body:         `{"test": true}`,
-		ContentType:  "application/json",
+		ContentType:  testContentType,
 	}
 	require.NoError(t, db.Create(event).Error)
 	assert.NotEmpty(t, event.ID)
@@ -99,7 +100,7 @@ func TestWebhookDBManager_CreateAndGetDB(t *testing.T) {
 		db.First(&readEvent, "id = ?", event.ID).Error,
 	)
 	assert.Equal(t, webhookID, readEvent.WebhookID)
-	assert.Equal(t, "POST", readEvent.Method)
+	assert.Equal(t, http.MethodPost, readEvent.Method)
 	assert.Equal(t, `{"test": true}`, readEvent.Body)
 }
 
@@ -123,9 +124,9 @@ func TestWebhookDBManager_DeleteDB(t *testing.T) {
 	event := &database.Event{
 		WebhookID:    webhookID,
 		EntrypointID: uuid.New().String(),
-		Method:       "POST",
+		Method:       http.MethodPost,
 		Body:         `{"test": true}`,
-		ContentType:  "application/json",
+		ContentType:  testContentType,
 	}
 	require.NoError(t, db.Create(event).Error)
 
@@ -196,10 +197,10 @@ func seedDeliveryWorkflow(
 	event := &database.Event{
 		WebhookID:    webhookID,
 		EntrypointID: uuid.New().String(),
-		Method:       "POST",
+		Method:       http.MethodPost,
 		Headers:      `{"Content-Type":["application/json"]}`,
 		Body:         `{"payload": "test"}`,
-		ContentType:  "application/json",
+		ContentType:  testContentType,
 	}
 	require.NoError(t, db.Create(event).Error)
 
@@ -231,7 +232,7 @@ func verifyPendingDeliveries(
 	)
 	require.Len(t, pending, 1)
 	assert.Equal(t, event.ID, pending[0].EventID)
-	assert.Equal(t, "POST", pending[0].Event.Method)
+	assert.Equal(t, http.MethodPost, pending[0].Event.Method)
 }
 
 func completeDelivery(
@@ -303,16 +304,16 @@ func TestWebhookDBManager_MultipleWebhooks(t *testing.T) {
 	event1 := &database.Event{
 		WebhookID:    webhook1,
 		EntrypointID: uuid.New().String(),
-		Method:       "POST",
+		Method:       http.MethodPost,
 		Body:         `{"webhook": 1}`,
-		ContentType:  "application/json",
+		ContentType:  testContentType,
 	}
 	event2 := &database.Event{
 		WebhookID:    webhook2,
 		EntrypointID: uuid.New().String(),
-		Method:       "PUT",
+		Method:       http.MethodPut,
 		Body:         `{"webhook": 2}`,
-		ContentType:  "application/json",
+		ContentType:  testContentType,
 	}
 
 	require.NoError(t, db1.Create(event1).Error)