Add webhook logging, pagination, middleware, migrations, and prod hardening

- Webhook event logging repo and subscription webhook idempotency
- Pagination helper (echohelpers) with cursor/offset support
- Request ID and structured logging middleware
- Push client improvements (FCM HTTP v1, better error handling)
- Task model version column, business constraint migrations, targeted indexes
- Expanded categorization chain tests
- Email service and config hardening
- CI workflow updates, .gitignore additions, .env.example updates

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/worker/jobs/handler.go

@@ -542,6 +542,11 @@ func NewSendPushTask(userID uint, title, message string, data map[string]string)
 // 2. Users who created a residence 5+ days ago but haven't created any tasks
 // Each email type is only sent once per user, ever.
 func (h *Handler) HandleOnboardingEmails(ctx context.Context, task *asynq.Task) error {
+	if !h.config.Features.OnboardingEmailsEnabled {
+		log.Debug().Msg("Onboarding emails disabled by feature flag, skipping")
+		return nil
+	}
+
 	log.Info().Msg("Processing onboarding emails...")
 
 	if h.onboardingService == nil {