feat(KB-026): add ntfy.sh push notification support

- Add ntfy settings (ntfyEnabled, ntfyTopic) to core types and config storage
- Create NtfyNotifier service with event-based notifications for task completion/failure
- Add Notifications section to SettingsModal for configuring ntfy topic
- Wire up NtfyNotifier in engine to send notifications on task state changes
- Include ntfy topic in task templates for per-task notification override
- Add comprehensive tests for NtfyNotifier service

packages/engine/src/index.ts

@@ -10,4 +10,4 @@ export { WorktreePool, scanIdleWorktrees, cleanupOrphanedWorktrees } from "./wor
 export { createLogger, type Logger } from "./logger.js";
 export { isUsageLimitError, UsageLimitPauser } from "./usage-limit-detector.js";
 export { PrMonitor, type PrComment, type TrackedPr, type OnNewCommentsCallback } from "./pr-monitor.js";
-export { PrCommentHandler } from "./pr-comment-handler.js";
+export { NtfyNotifier, type NtfyNotifierOptions } from "./notifier.js";