fix: comprehensive system audit fixes (55+ issues)

CRITICAL:
- Fix SQL injection in prestart.sh (parameterized query)
- Fix secret key validation (always validate, not just production)
- Fix workspace model partial index bug (func.text -> text)
- Fix HealthResponse schema (add checks field)
- Fix Tenant import in permissions.py (NameError on every auth request)
- Fix README tech stack (React instead of Alpine.js)
- Delete broken test_cross_tenant_security_v2.py
- Add fail-closed RLS migration 0084 (48 tenant tables)

HIGH:
- Add GeneralRateLimitMiddleware for all API routes
- Add file type blocklist for DMS and attachment uploads
- Fix guest auth: Pydantic schema, tenant_slug required, CSRF bypass
- Fix CSRF bypass path matching (in -> endswith)
- Add worker healthcheck in docker-compose.yml
- Add ARQ max_tries=3 for job retries
- Fix 28 bare pass in mail services (-> logger.debug)
- Fix print() -> logger in main.py and ai_assistant
- Fix duplicate email handling (catch IntegrityError -> 409)
- Add session revocation (invalidate_all_user_sessions)
- Add resource limits to all containers
- Fix CORS default (localhost -> production domain)
- Fix SameSite=Lax -> Strict
- Fix Redis password visibility in healthcheck
- Fix npm vulnerabilities (19 -> 9)
- Fix Sidebar OOM (wildcard lucide import -> curated ICON_MAP)

MEDIUM:
- Localize ErrorBoundary to German
- Wire Mail.tsx save/delete filter to API
- Document system_notif plugin (no routes needed)
- Fix datetime.utcnow() -> datetime.now(UTC)
- Pin litellm version (>=1.0,<2.0)
- Move CSRF token from sessionStorage to in-memory
- Fix restore_backup error handling and transaction
- Fix Dms.tsx useEffect cleanup
- Add skip-to-content link for accessibility
- Add selectinload imports to 3 services
- Add .env.example missing variables
- Fix AppShell/TopBar/Sidebar test mocks

NEW TESTS:
- test_guest_auth.py (6 tests)
- test_user_service.py (8 tests)
- test_backup_service.py (5 tests)

NEW SCHEMAS:
- saved_filter, saved_view, user_preference, workspace, entity_policy

Tests: 22/22 PASSED

frontend/src/components/common/ErrorBoundary.tsx

@@ -58,14 +58,14 @@ export class ErrorBoundary extends Component<ErrorBoundaryProps, ErrorBoundarySt
           }}
         >
           <h2 style={{ marginBottom: '0.5rem', color: '#dc2626' }}>
-            Something went wrong
+            Etwas ist schiefgelaufen
           </h2>
           <p style={{ marginBottom: '1rem', color: '#6b7280', maxWidth: '400px' }}>
-            An unexpected error occurred. You can try again or refresh the page.
+            Ein unerwarteter Fehler ist aufgetreten. Sie können es erneut versuchen oder die Seite aktualisieren.
           </p>
           <details style={{ marginBottom: '1rem', maxWidth: '600px', color: '#9ca3af' }}>
             <summary style={{ cursor: 'pointer', fontSize: '0.875rem' }}>
-              Error details
+              Fehlerdetails
             </summary>
             <pre
               style={{
@@ -92,7 +92,7 @@ export class ErrorBoundary extends Component<ErrorBoundaryProps, ErrorBoundarySt
               fontWeight: 500,
             }}
           >
-            Retry
+            Erneut versuchen
           </button>
         </div>
       );