Update golangci-lint to v2.12.2 with canonical config

Bump golangci-lint from v2.10.1 to v2.12.2 in the Dockerfile lint
stage (tag+digest pin) and script/bootstrap release-archive pins
(linux amd64/arm64 sha256s). Replace .golangci.yml with the canonical
v2-layout config so linter settings (lll 88, funlen 80/50, cyclop 15,
dupl 100) actually apply.

Fix all findings surfaced by the new linter and config:

- noctx: use httptest.NewRequestWithContext in all tests
- gosec G710/G703: route app redirects through a path-escaping
  redirectToApp helper; annotate internal log path usage
- goconst: introduce shared constants for template/JSON keys and
  repeated test literals
- lll: wrap lines to the 88-column limit
- dupl: extract shared helpers (generic findAllByAppID in models,
  deleteAppResource in handlers, parsePush in webhook payloads,
  table-driven/helper-based test dedup)
- nolintlint: drop nolint directives made obsolete by the new limits

Record the change in TODO.md; make check is green.

internal/service/notify/notify.go

@@ -159,7 +159,8 @@ func (svc *Service) NotifyDeployFailed(
 ) {
 	duration := time.Since(deployment.StartedAt)
 	title := "Deploy failed: " + app.Name
-	message := "Deployment failed after " + formatDuration(duration) + ": " + deployErr.Error()
+	message := "Deployment failed after " + formatDuration(duration) +
+		": " + deployErr.Error()
 
 	svc.sendNotifications(ctx, app, title, message, message, "error")
 }
@@ -266,7 +267,8 @@ func (svc *Service) sendNtfy(
 	request.Header.Set("Title", title)
 	request.Header.Set("Priority", svc.ntfyPriority(priority))
 
-	resp, err := svc.client.Do(request) // #nosec G704 -- URL from validated config, not user input
+	// #nosec G704 -- URL from validated config, not user input
+	resp, err := svc.client.Do(request)
 	if err != nil {
 		return fmt.Errorf("failed to send ntfy request: %w", err)
 	}
@@ -363,7 +365,8 @@ func (svc *Service) sendSlack(
 
 	request.Header.Set("Content-Type", "application/json")
 
-	resp, err := svc.client.Do(request) // #nosec G704 -- URL from validated config, not user input
+	// #nosec G704 -- URL from validated config, not user input
+	resp, err := svc.client.Do(request)
 	if err != nil {
 		return fmt.Errorf("failed to send slack request: %w", err)
 	}