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/create-flows/HANDOFF.md

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+# Create flows — handoff
+
+## Summary
+
+UI for creating rooms, spaces, direct chats, and adding existing rooms to spaces. Includes modal renderers mounted at client root and join/create page routes.
+
+## User-facing behavior
+
+- Create room modal (optionally as sub-room of parent)
+- Create space modal
+- Create DM / group DM
+- Add existing room to space
+- Create tab in sidebar for quick actions
+
+## Architecture
+
+```
+CreateRoomModalRenderer → CreateRoomModal.tsx
+CreateSpaceModalRenderer → CreateSpaceModal.tsx
+create-chat/ — DM creation
+add-existing/ — pick room to add to space
+pages/client/create/Create.tsx — create hub
+pages/client/direct/DirectCreate.tsx
+State: createRoomModal.ts, createSpaceModal.ts
+```
+
+## Key files
+
+| Path | Role |
+|------|------|
+| `cinny/src/app/features/create-room/CreateRoomModal.tsx` | Room create + sub-room parent update |
+| `cinny/src/app/features/create-space/CreateSpaceModal.tsx` | Space create |
+| `cinny/src/app/features/create-chat/` | DM flows |
+| `cinny/src/app/features/add-existing/AddExisting.tsx` | Add to space |
+| `cinny/src/app/features/create-room/CreateRoom.tsx` | Standalone create page |
+| `cinny/src/app/features/create-space/CreateSpace.tsx` | Standalone space create |
+| `cinny/src/app/state/createRoomModal.ts` | Modal state + parent room id |
+| `cinny/src/app/state/createSpaceModal.ts` | Space modal state |
+| `cinny/src/app/pages/client/create/Create.tsx` | Create hub route |
+| `cinny/src/app/pages/client/home/CreateRoom.tsx` | Home create entry |
+
+## Data model
+
+Creates standard Matrix rooms/spaces. Sub-room creation also updates `im.paarrot.sub_rooms` on parent.
+
+## Dependencies
+
+- matrix-js-sdk `createRoom` APIs
+- Space parent/child events
+
+## Integration points
+
+- **sub-rooms**: parent id in create room modal
+- **room-nav**: opens create sub-room modal
+- **routing-and-navigation**: Create routes, modal renderers
+
+## Testing
+
+### Manual
+
+1. Create public room; verify join.
+2. Create sub-room under parent; appears in home tree.
+3. Create space; add existing room.
+4. Start DM from DirectCreate.
+
+### Automated
+
+- None
+
+## Known issues & gotchas
+
+- Sub-room failure after room created leaves orphan — see sub-rooms handoff
+- `CreateRoomKindSelector` for room type variants
+- Forum room type may need specific create options
+
+## Future work
+
+- Create forum space template
+- Batch add rooms to space
+
+## Related docs
+
+- [sub-rooms HANDOFF](../sub-rooms/HANDOFF.md)
+- [routing-and-navigation HANDOFF](../routing-and-navigation/HANDOFF.md)
+
+## Add your extra things here
+
+- `useOpenCreateSubRoomModal` hook opens modal with `parentRoomId`