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/testutil/testutil.go

@@ -208,6 +208,7 @@ func CreateTestTask(t *testing.T, db *gorm.DB, residenceID, createdByID uint, ti
 		Title:       title,
 		IsCancelled: false,
 		IsArchived:  false,
+		Version:     1,
 	}
 	err := db.Create(task).Error
 	require.NoError(t, err)