feat(11-01): per-library scan pipeline with queue coordinator

Task 1: Schema, events, and progress types
- Add library_id to CreateAudioFile SQL INSERT and regenerate sqlc code
- Add LibraryScanQueued and LibraryScanQueueDrained event constants
- Regenerate TypeScript events via genevents
- Add LibraryID, LibraryName, QueuedCount to ScanProgress
- Add LibraryID, LibraryName to ScanMetrics
- Add libraryID field to importResult for threading through pipeline

Task 2: Scan queue coordinator and per-library scanning
- Create scan_queue.go with ScanLibrary(id), ScanAllLibraries()
- Add CancelCurrentScan(), CancelAllScans() for queue-aware cancellation
- FIFO scan queue with silent dedup (same library already scanning or queued)
- Refactor Scan() -> scanInternal(libraryID, libraryName, libraryPath)
- Replace GetAllAudioFiles with GetAudioFilesByLibrary for per-library loading
- Thread libraryID through DB writer to set CreateAudioFileParams.LibraryID
- drainQueue auto-starts next queued library or emits LibraryScanQueueDrained
- Pause freezes current scan AND queue
- Add GetScanQueueLength() and QueuedLibraryNames() for UI
- Mark CancelScan() and Scan() as deprecated

frontend/wailsjs/go/models.ts

@@ -109,6 +109,8 @@ export namespace library {
 	    skipped: number;
 	    removed: number;
 	    cancelled: boolean;
+	    libraryId: number;
+	    libraryName: string;
 	    warnings: ScanWarning[];
 	
 	    static createFrom(source: any = {}) {
@@ -143,6 +145,8 @@ export namespace library {
 	        this.skipped = source["skipped"];
 	        this.removed = source["removed"];
 	        this.cancelled = source["cancelled"];
+	        this.libraryId = source["libraryId"];
+	        this.libraryName = source["libraryName"];
 	        this.warnings = this.convertValues(source["warnings"], ScanWarning);
 	    }