feat: move configuration from .env to DB with Admin UI management

Replace hardcoded .env configuration with database-backed settings
manageable through the Admin web interface. This reduces .env to
bootstrap-only variables (DB, Keycloak, encryption keys).

Backend:
- Add SystemSetting Prisma model with category, valueType, isSecret
- Add system-settings NestJS module (CRUD, 60s cache, encryption)
- Refactor all 7 connectors to lazy-load credentials from DB via
  CredentialsService.findActiveByType() instead of ConfigService
- Add event-driven credential reload (@nestjs/event-emitter)
- Dynamic CORS origins and conditional Swagger from DB settings
- Fix JWT strategy: use Keycloak JWKS (RS256) instead of symmetric secret
- Add SYSTEM_SETTINGS_VIEW/MANAGE permissions
- Seed 13 default settings (sync intervals, features, branding, CORS)
- Add env-to-db migration script (prisma/migrate-env-to-db.ts)

Frontend:
- Add use-credentials hook (full CRUD for integration credentials)
- Add use-system-settings hook (read/update system settings)
- Wire admin-integrations page to real API (create/update/test/toggle)
- Add admin system-settings page with 4 tabs (Branding, CORS, Sync, Features)
- Fix sidebar double-highlighting with exactMatch flag
- Fix integration detail fallback when API unavailable
- Fix API client to unwrap backend's {success, data} envelope
- Update NEXT_PUBLIC_API_URL to include /v1 version prefix
- Fix activity-widget hydration error
- Add i18n keys for systemSettings (de + en)

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

apps/web/src/lib/api.ts

@@ -59,7 +59,12 @@ async function request<T>(endpoint: string, config: RequestConfig = {}): Promise
   // Handle empty responses
   const contentType = response.headers.get('content-type');
   if (contentType?.includes('application/json')) {
-    return response.json();
+    const json = await response.json();
+    // Unwrap backend's {success, data, timestamp} envelope
+    if (json && typeof json === 'object' && 'success' in json && 'data' in json) {
+      return json.data as T;
+    }
+    return json as T;
   }
 
   return {} as T;