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/space-settings/HANDOFF.md

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+# Space settings — handoff
+
+## Summary
+
+Per-space settings overlay analogous to room settings: general space profile, permissions, and shared common-settings pages. Used for Matrix spaces (and forum spaces).
+
+## User-facing behavior
+
+- Edit space name, topic, avatar, visibility
+- Space permissions and power levels
+- Child space management via common flows
+
+## Architecture
+
+```
+SpaceSettingsRenderer (Router overlay)
+  → space-settings/SpaceSettings.tsx
+  → general/, permissions/
+spaceSettings.ts atom
+```
+
+## Key files
+
+| Path | Role |
+|------|------|
+| `cinny/src/app/features/space-settings/SpaceSettings.tsx` | Settings shell |
+| `cinny/src/app/features/space-settings/general/` | General tab |
+| `cinny/src/app/features/space-settings/permissions/` | Permissions |
+| `cinny/src/app/state/spaceSettings.ts` | Open state |
+| `cinny/src/app/state/hooks/spaceSettings.ts` | Hooks |
+
+## Data model
+
+Matrix space state: `m.space.child`, `m.room.name`, power levels, etc.
+
+## Dependencies
+
+- Same permission patterns as room settings
+
+## Integration points
+
+- **lobby-forums**: space metadata shown in lobby hero
+- **create-flows**: add existing rooms to space
+- **common-settings**: shared pages
+
+## Testing
+
+### Manual
+
+1. Open space settings.
+2. Edit space name and avatar.
+3. Change join rules / visibility.
+
+### Automated
+
+- None
+
+## Known issues & gotchas
+
+- Forum spaces may expose different settings entry points — verify `ForumSpaceLayout`
+
+## Future work
+
+- Space-level embed filter defaults
+
+## Related docs
+
+- [common-settings HANDOFF](../common-settings/HANDOFF.md)
+- [lobby-forums HANDOFF](../lobby-forums/HANDOFF.md)
+
+## Add your extra things here
+
+- `usePermissionItems` in space-settings/permissions/