feat: upgrade toolchain and soften sync recovery after network blips

Bump Vite 8, matrix-js-sdk, and related deps; fix immer/vanilla-extract imports for new majors. Replace blocking sync error dialog with background recovery on wake/offline, and disable Vite auto-open in dev. Add feature handoff documentation index.

docs/handoff/features/android/HANDOFF.md

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+# Android (Capacitor / Tauri) — handoff
+
+## Summary
+
+Paarrot ships an Android build via Capacitor and/or Tauri (`src-tauri/`, `cinny/capacitor.config.json`). Mobile-specific code handles native notifications, UnifiedPush background sync, share intents, and platform detection branching away from Electron APIs.
+
+## User-facing behavior
+
+- Native Android app with Paarrot UI (WebView)
+- Share into Paarrot from other apps (images/files → room upload draft)
+- Background notifications via UnifiedPush (not FCM-only)
+- No local HTTP API on mobile (Electron-only)
+
+## Architecture
+
+```
+Capacitor/Tauri shell
+  → WebView loads cinny bundle
+ClientNonUIFeatures.tsx
+  → isCapacitorNative / isTauri branches
+backgroundSync.ts → UnifiedPush + Matrix pusher
+androidShare.ts → share intent → room draft
+tauri.ts → native notification APIs
+```
+
+## Key files
+
+| Path | Role |
+|------|------|
+| `cinny/capacitor.config.json` | Capacitor app id, web dir |
+| `src-tauri/src/main.rs` | Tauri Android entry |
+| `cinny/src/app/utils/tauri.ts` | Platform detection, notifications |
+| `cinny/src/app/utils/backgroundSync.ts` | UnifiedPush registration |
+| `cinny/src/app/utils/androidShare.ts` | Share target handling |
+| `cinny/src/app/pages/client/ClientNonUIFeatures.tsx` | Share listener wiring |
+
+## Data model
+
+Same as background notifications (`paarrot.unifiedpush.*` localStorage).
+
+Share payloads: ephemeral in-memory until user picks room.
+
+## Dependencies
+
+- Capacitor plugins / Tauri mobile toolchain
+- UnifiedPush distributor (ntfy, etc.)
+- Android notification icon resources
+
+## Integration points
+
+- **background-notifications**: primary overlap
+- **Room input drafts**: `roomIdToUploadItemsAtomFamily` for shared files
+- **NOT Electron**: `initPaarrotAPI` skips on mobile webview
+
+## Testing
+
+### Manual
+
+1. Build Android APK/AAB per project scripts.
+2. Share image from Gallery → Paarrot → pick room → verify upload draft.
+3. Background app; trigger mention; verify UP notification.
+4. Tap notification → opens correct room.
+
+### Automated
+
+- None on device CI in repo (check Gitea workflow)
+
+## Known issues & gotchas
+
+- `ANDROID_NOTIFICATION_SMALL_ICON = 'ic_stat_paarrot'` must exist in Android res
+- UnifiedPush without distributor shows user-facing error string
+- Feature parity gap vs desktop (plugins, Stream Deck, local API)
+- Test `isTauri` vs `isCapacitorNative` — both may be true in some builds
+
+## Future work
+
+- iOS Capacitor target
+- Play Store release pipeline docs
+- Mobile plugin sandbox policy
+
+## Related docs
+
+- [background-notifications HANDOFF](../background-notifications/HANDOFF.md)
+
+## Add your extra things here
+
+- `listenForAndroidShares`, `getPendingAndroidShare`, `materializeSharedFile` in `androidShare.ts`
+- Capacitor app name in `capacitor.config.json` — verify `appId` matches push config