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>

.env.example

@@ -40,17 +40,22 @@ APNS_PRODUCTION=false  # Set to true for production APNs, false for sandbox
 # Direct FCM integration using legacy HTTP API
 FCM_SERVER_KEY=your-firebase-server-key
 
-# Worker Settings (Background Jobs)
-TASK_REMINDER_HOUR=20
-TASK_REMINDER_MINUTE=0
-OVERDUE_REMINDER_HOUR=9
-DAILY_DIGEST_HOUR=11
-
-# Admin Panel
-ADMIN_PORT=9000
+# Worker Settings (Background Jobs - UTC hours)
+TASK_REMINDER_HOUR=14
+OVERDUE_REMINDER_HOUR=15
+DAILY_DIGEST_HOUR=3
 
 # Storage Settings (File Uploads)
 STORAGE_UPLOAD_DIR=./uploads
 STORAGE_BASE_URL=/uploads
 STORAGE_MAX_FILE_SIZE=10485760
 STORAGE_ALLOWED_TYPES=image/jpeg,image/png,image/gif,image/webp,application/pdf
+
+# Feature Flags (Kill Switches)
+# Set to false to disable. All default to true (enabled).
+FEATURE_PUSH_ENABLED=true
+FEATURE_EMAIL_ENABLED=true
+FEATURE_WEBHOOKS_ENABLED=true
+FEATURE_ONBOARDING_EMAILS_ENABLED=true
+FEATURE_PDF_REPORTS_ENABLED=true
+FEATURE_WORKER_ENABLED=true