perf(11-02): lazy-load non-critical routes — PERF-03
- Keep FileManagerView synchronous for / per D-10 (critical first authenticated surface)
- Lazy-load TopicsView, DocumentView, SettingsView, CloudStorageView, CloudFolderView
- /folders/:folderId reuses synchronous FileManagerView (no split, same component)
- Main bundle reduced from 264.63 kB to 180.17 kB (split into 5 new route chunks)
- Extend router guard tests: admin child route blocking, refresh-before-guard flow,
lazy-loaded route resolution — 234 tests pass (15 new tests added)