feat(FN-2878): add webhook notification provider support

- Add webhook settings fields and defaults for enablement, URL, format, and event filtering
- Implement WebhookNotificationProvider with payload formatting support for generic, Slack, and Discord endpoints
- Extend NotificationService to manage both ntfy and webhook providers with live settings sync
- Export webhook notification types/providers through engine notification entry points

packages/engine/src/index.ts

@@ -66,8 +66,8 @@ export {
   type SendNtfyNotificationInput,
 } from "./notifier.js";
 // ── Notification Service ──────────────────────────────────────
-export { NtfyNotificationProvider, NotificationService } from "./notification/index.js";
-export type { NtfyProviderConfig, NotificationServiceOptions } from "./notification/index.js";
+export { NtfyNotificationProvider, NotificationService, WebhookNotificationProvider } from "./notification/index.js";
+export type { NtfyProviderConfig, NotificationServiceOptions, WebhookProviderConfig } from "./notification/index.js";
 export { CronRunner, type CronRunnerOptions, type AiPromptExecutor, createAiPromptExecutor } from "./cron-runner.js";
 export { RoutineRunner, type RoutineRunnerOptions } from "./routine-runner.js";
 export { RoutineScheduler, type RoutineSchedulerOptions } from "./routine-scheduler.js";