🔧 feat: add OpenTelemetry instrumentation to persistence layer

- Added persistence telemetry configuration option (telemetry.persistence.enabled)
- Created PersistenceTelemetryConfig struct for fine-grained control
- Added GetPersistenceTelemetryEnabled() helper method
- Implemented telemetry span creation in SQLite repository
- Added OpenTelemetry instrumentation to key repository methods:
  - CreateUser: Tracks user creation with error recording
  - GetUserByUsername: Tracks queries with username attribute
- Maintained backward compatibility - telemetry is optional and disabled by default
- Updated all tests to pass config parameter to repository constructor
- Added proper error recording and span attributes for observability

Benefits:
- Performance monitoring of database operations
- Flamegraph generation capability for persistence layer
- Distributed tracing across service boundaries
- Configurable instrumentation for production vs development

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

pkg/server/server.go

@@ -77,7 +77,7 @@ func initializeUserServices(cfg *config.Config) (user.UserRepository, user.UserS
 	dbPath := "file::memory:?cache=shared"
 
 	// Create user repository
-	repo, err := user.NewSQLiteRepository(dbPath)
+	repo, err := user.NewSQLiteRepository(dbPath, cfg)
 	if err != nil {
 		return nil, nil, fmt.Errorf("failed to create user repository: %w", err)
 	}