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/room-nav/HANDOFF.md

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+# Room nav — handoff
+
+## Summary
+
+Room nav components render individual channel rows in sidebars and space channel lists: room items, category buttons, call participant indicators, sub-room actions, and unjoined sub-room join prompts.
+
+## User-facing behavior
+
+- Room row: name, avatar, unread badge, active highlight
+- Context menu: add sub-room, room actions
+- Call participants indicator when call active in room
+- Unjoined sub-room row with join button
+- Category headers with collapse
+
+## Architecture
+
+```
+features/room-nav/
+  RoomNavItem → per-room row + menus
+  RoomNavCategoryButton → section headers
+  UnjoinedSubRoomItem → join flow
+  CallParticipantsIndicator → active call badge
+Used by Home.tsx, space sidebars, forum sidebars
+```
+
+## Key files
+
+| Path | Role |
+|------|------|
+| `cinny/src/app/features/room-nav/RoomNavItem.tsx` | Main room row |
+| `cinny/src/app/features/room-nav/RoomNavCategoryButton.tsx` | Category header |
+| `cinny/src/app/features/room-nav/UnjoinedSubRoomItem.tsx` | Unjoined sub-room |
+| `cinny/src/app/features/room-nav/CallParticipantsIndicator.tsx` | In-call indicator |
+| `cinny/src/app/features/room-nav/styles.css.ts` | Nav styles |
+
+## Data model
+
+Uses room state, unread atoms, `im.paarrot.sub_rooms` permissions — no own persistence.
+
+## Dependencies
+
+- `usePermission` for sub-room create
+- `useOpenCreateSubRoomModal` from state hooks
+
+## Integration points
+
+- **sub-rooms**: Add Sub-Room menu action
+- **voice-calls**: participant indicator
+- **create-flows**: opens create room modal with parent id
+- **home-and-sidebar**: primary consumer
+
+## Testing
+
+### Manual
+
+1. Right-click/context menu on room row.
+2. Add sub-room when permitted / disabled when not.
+3. Active call shows participant indicator.
+4. Unjoined sub-room join navigates correctly.
+
+### Automated
+
+- None
+
+## Known issues & gotchas
+
+- Depth indentation for sub-rooms passed as prop — styling in CSS
+- `canAddSubRoom` checks `StateEvent.PaarrotSubRooms` power level
+
+## Future work
+
+- Consolidate with forum sidebar items if duplicated
+
+## Related docs
+
+- [sub-rooms HANDOFF](../sub-rooms/HANDOFF.md)
+- [home-and-sidebar HANDOFF](../home-and-sidebar/HANDOFF.md)
+- [voice-calls HANDOFF](../voice-calls/HANDOFF.md)
+
+## Add your extra things here
+
+- Export barrel: `features/room-nav/index.ts`