feat: theme config service — REST API with versioning + backup

- ThemeService: read/write/validate theme.json, auto-backup on save
- ThemeController: GET/PUT/POST /api/config/theme (public GET, versioned PUT)
- ThemeConfig type with version + updatedAt fields
- Default theme: Global Hospital blue scale
- ConfigThemeModule registered in AppModule

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/app.module.ts

@@ -18,6 +18,7 @@ import { RecordingsModule } from './recordings/recordings.module';
 import { EventsModule } from './events/events.module';
 import { CallerResolutionModule } from './caller/caller-resolution.module';
 import { RulesEngineModule } from './rules-engine/rules-engine.module';
+import { ConfigThemeModule } from './config/config-theme.module';
 
 @Module({
     imports: [
@@ -42,6 +43,7 @@ import { RulesEngineModule } from './rules-engine/rules-engine.module';
         EventsModule,
         CallerResolutionModule,
         RulesEngineModule,
+        ConfigThemeModule,
     ],
 })
 export class AppModule {}