Align ConfigManager with DataSync's per-file pipeline format (pipeline.*.json)
by reusing EtlPipelineConfig types directly, eliminating duplicate models and
simplifying the codebase. Removes ~3200 lines of obsolete code.
- SearchRepository: Search table operations with Dapper
- SearchExecutionService: Search pipeline with proper cancellation handling
- WorkProcessor: Unified BackgroundService for syncs and searches
- SearchNotificationService: SignalR notifications in Api layer
All 45 new tests pass. Proper shutdown vs timeout distinction
prevents marking searches as error on host shutdown.