feat(ios): add iOS platform support via Capacitor

Add iOS MVP with core functionality using Capacitor-first approach:

Platform Abstraction Layer:
- Add CapacitorPlatformService for unified platform detection
- Add PlatformCapabilities model with per-platform feature flags
- Add CapacitorNotificationService wrapping LocalNotifications plugin
- Add CapacitorReminderService for cross-platform reminder scheduling

iOS Support:
- Add Capacitor iOS project with proper configuration
- Configure Info.plist for notifications and background modes
- Add app icon and splash screen assets
- Enable CapacitorHttp for WebDAV sync (avoids CORS issues)

Refactoring:
- Update android.effects.ts to use CapacitorReminderService
- Update notify.service.ts to support iOS notifications
- Update startup.service.ts with platform-aware initialization
- Update sync-form.const.ts to hide CORS info on native platforms
- Update webdav-http-adapter.ts to use CapacitorHttp on iOS

MVP includes: task management, scheduled notifications, Dropbox sync,
WebDAV sync, share-out, dark mode. Excludes: background tracking,
widgets, local file sync, share-in (post-MVP features).

package.json

@@ -136,6 +136,7 @@
     "@ctrl/tinycolor": "4.1.0"
   },
   "dependencies": {
+    "@capacitor/ios": "^7.4.4",
     "electron-dl": "^3.5.2",
     "electron-localshortcut": "^3.2.1",
     "electron-log": "^5.4.3",