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/api/src/modules/system-settings/dto/update-setting.dto.ts

@@ -0,0 +1,53 @@
+import { ApiProperty, ApiPropertyOptional } from '@nestjs/swagger';
+import { IsString, IsOptional, IsBoolean } from 'class-validator';
+
+export class UpdateSettingDto {
+  @ApiProperty({ description: 'The setting value (always stored as string)' })
+  @IsString()
+  value: string;
+
+  @ApiPropertyOptional({ description: 'Human-readable description of the setting' })
+  @IsString()
+  @IsOptional()
+  description?: string;
+
+  @ApiPropertyOptional({
+    description: 'Value type for parsing: string, number, boolean, json',
+    enum: ['string', 'number', 'boolean', 'json'],
+  })
+  @IsString()
+  @IsOptional()
+  valueType?: string;
+
+  @ApiPropertyOptional({ description: 'Whether the value should be encrypted at rest' })
+  @IsBoolean()
+  @IsOptional()
+  isSecret?: boolean;
+}
+
+export class BulkUpdateSettingsDto {
+  @ApiProperty({
+    type: 'array',
+    items: {
+      type: 'object',
+      properties: {
+        key: { type: 'string' },
+        value: { type: 'string' },
+        category: { type: 'string' },
+        description: { type: 'string' },
+        valueType: { type: 'string' },
+        isSecret: { type: 'boolean' },
+      },
+      required: ['key', 'value'],
+    },
+    description: 'Array of settings to upsert in one transaction',
+  })
+  settings: Array<{
+    key: string;
+    value: string;
+    category?: string;
+    description?: string;
+    valueType?: string;
+    isSecret?: boolean;
+  }>;
+}