feat: native desktop notifications + rowboat:// deep links

Adds INotificationService with an Electron implementation, plus a deep-link
dispatcher (rowboat://) for routing notification clicks back into the app.

Notifications:
- New `notify-user` skill + builtin tool. Title, message, optional primary
    link, optional secondary actions. Supports https:// (opens in browser) and
    rowboat:// (opens in app) targets.
- ElectronNotificationService holds strong refs to active Notification
    instances so click handlers survive GC (otherwise macOS click silently
    no-ops).
- Calendar meeting notifier fires 1-min warnings with "take notes" /
    "join + take notes" actions backed by deep links.

Deep links (rowboat://):
- forge.config.cjs declares the protocol; main.ts wires single-instance
    lock, setAsDefaultProtocolClient, open-url (mac), second-instance (win/
    linux), and first-launch argv extraction.
- New deeplink.ts dispatcher with dispatchUrl(url): main-handled actions
    (rowboat://action?type=...) vs renderer navigation (rowboat://open?...)
    via app:openUrl IPC. Includes pending-URL buffering for first-launch
    delivery before the renderer is ready.
- Renderer parseDeepLink supports file / chat / graph / task /
    suggested-topics targets.
- New app:consumePendingDeepLink IPC for renderer one-time drain on mount.

Refactor: extractConferenceLink moved out of calendar-block.tsx into
shared lib/calendar-event.ts (used by both the block and the take-notes
deep-link handler)

apps/x/apps/main/forge.config.cjs

@@ -11,6 +11,9 @@ module.exports = {
         icon: './icons/icon',  // .icns extension added automatically
         appBundleId: 'com.rowboat.app',
         appCategoryType: 'public.app-category.productivity',
+        protocols: [
+            { name: 'Rowboat', schemes: ['rowboat'] },
+        ],
         extendInfo: {
             NSAudioCaptureUsageDescription: 'Rowboat needs access to system audio to transcribe meetings from other apps (Zoom, Meet, etc.)',
         },