FRE-4510: Add voiceprint feature flag support

- Create voiceprint.feature-flags.ts to re-export checkFlag
- Update voiceprint.config.ts to use checkFlag for all flags
- Update voiceprint.service.ts to import checkFlag
- Ensure voiceprint services respect feature flags

apps/api/src/services/voiceprint/voiceprint.service.ts

@@ -5,7 +5,9 @@ import {
   DetectionType,
   ConfidenceLevel,
   audioPreprocessingConfig,
+  voicePrintFeatureFlags,
 } from './voiceprint.config';
+import { checkFlag } from './voiceprint.feature-flags';
 
 // Audio preprocessing service
 export class AudioPreprocessor {