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/global-search/HANDOFF.md

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+# Global search — handoff
+
+## Summary
+
+Quick global search modal for jumping to rooms, users, and recent conversations. Distinct from full message search — optimized for navigation, not event content search.
+
+## User-facing behavior
+
+- Keyboard shortcut / sidebar tab opens search modal
+- Type to filter rooms and users
+- Select result to navigate
+
+## Architecture
+
+```
+SearchModalRenderer (in Router.tsx)
+  → features/search/Search.tsx
+  → searchModal.ts atom for open state
+useAsyncSearch or similar for filtering
+```
+
+## Key files
+
+| Path | Role |
+|------|------|
+| `cinny/src/app/features/search/Search.tsx` | Modal UI |
+| `cinny/src/app/state/searchModal.ts` | Open/close state |
+| `cinny/src/app/pages/client/sidebar/SearchTab.tsx` | Sidebar entry |
+
+## Data model
+
+| Key | Storage |
+|-----|---------|
+| `searchModal` atom | memory |
+
+## Dependencies
+
+- Local room list + user index from sync
+
+## Integration points
+
+- **routing-and-navigation**: `SearchModalRenderer` in router
+- **home-and-sidebar**: SearchTab
+- **message-search**: different feature — don't merge UIs
+
+## Testing
+
+### Manual
+
+1. Open search modal from sidebar.
+2. Filter rooms by name.
+3. Select room; navigates and modal closes.
+
+### Automated
+
+- None
+
+## Known issues & gotchas
+
+- Two "search" features confuse users — message search vs global nav search
+- Modal focus trap via folds Overlay patterns
+
+## Future work
+
+- Unify search entry points with tabs (rooms / messages / users)
+- Recent searches persistence
+
+## Related docs
+
+- [message-search HANDOFF](../message-search/HANDOFF.md)
+- [routing-and-navigation HANDOFF](../routing-and-navigation/HANDOFF.md)
+
+## Add your extra things here
+
+- `SearchModalRenderer` mounted at client root level in Router.tsx