feat: Phase 4+5 — admin storage UI, backend proxy, CLAUDE.md enforcement

- backend/app/routers/storage_config.py: 5 admin-only endpoints proxying
  storage-service config + migration API (GET/PATCH/POST/DELETE)
- backend/app/main.py: register storage_config router
- frontend/src/api/client.ts: StorageStatus, MigrationStatus,
  StorageBackendConfig interfaces + 5 API functions
- frontend/src/pages/StorageAdminPage.tsx: full admin UI — backend health
  dot, driver selector (local/S3/WebDAV), conditional credential fields,
  Test & Migrate button, live 2s-poll migration progress bar, Cancel
- frontend/src/App.tsx: /admin/storage route (AdminRoute guard)
- CLAUDE.md: storage enforcement rule, updated Docker tables (6 services,
  3 volumes), §20 in merge checklist
- backend/CLAUDE.md, frontend/CLAUDE.md, doc-service/CLAUDE.md,
  ai-service/CLAUDE.md: updated to reflect storage-service integration
- tests/ALL_TESTS.md + tests/storage-service_tests.md: §20 (20 tests)
- backend/STATUS.md, frontend/STATUS.md: updated with new endpoints/routes
- changelog/2026-04-20_storage-service.md: full change log

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/CLAUDE.md

@@ -37,7 +37,8 @@ frontend/
 │   │   └── ui/                        ← shadcn/ui components (Button, Input, …)
 │   ├── pages/                         ← One file per route
 │   │   ├── DocServiceSettingsPage.tsx ← Combined doc-service settings: upload limits + watch directory
-│   │   └── PluginSettingsPage.tsx     ← Generic plugin settings page driven by manifest
+│   │   ├── PluginSettingsPage.tsx     ← Generic plugin settings page driven by manifest
+│   │   └── StorageAdminPage.tsx       ← Admin storage backend config + live migration progress
 │   ├── lib/utils.ts                   ← cn() = clsx + tailwind-merge
 │   └── styles/theme.css               ← CSS custom properties, Tailwind setup
 ├── vite.config.ts                     ← /api/* proxied to backend:8000
@@ -66,6 +67,7 @@ frontend/
 | `/admin/users` | `AdminUsersPage` | AdminRoute |
 | `/admin/groups` | `AdminGroupsPage` | AdminRoute |
 | `/admin/appearance` | `AdminAppearancePage` | AdminRoute |
+| `/admin/storage` | `StorageAdminPage` | AdminRoute |
 | `*` | redirect to `/` | — |
 
 `PrivateRoute` — checks `token` from `useAuth`, redirects to `/login` if absent.