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/library/Library.d.ts

@@ -3,6 +3,10 @@
 import {library} from '../models';
 import {context} from '../models';
 
+export function CancelAllScans():Promise<void>;
+
+export function CancelCurrentScan():Promise<void>;
+
 export function CancelScan():Promise<void>;
 
 export function FullRescan():Promise<library.ScanMetrics>;
@@ -19,6 +23,8 @@ export function GetAllGenresWithCounts():Promise<Array<library.GenreWithCount>>;
 
 export function GetAllTracks():Promise<Array<library.Track>>;
 
+export function GetScanQueueLength():Promise<number>;
+
 export function GetTracksByGenre(arg1:string):Promise<Array<library.Track>>;
 
 export function IsScanActive():Promise<boolean>;
@@ -27,10 +33,16 @@ export function IsScanPaused():Promise<boolean>;
 
 export function PauseScan():Promise<void>;
 
+export function QueuedLibraryNames():Promise<Array<string>>;
+
 export function ResumeScan():Promise<void>;
 
 export function Scan():Promise<library.ScanMetrics>;
 
+export function ScanAllLibraries():Promise<void>;
+
+export function ScanLibrary(arg1:number):Promise<void>;
+
 export function SearchTracks(arg1:string):Promise<Array<library.Track>>;
 
 export function SetContext(arg1:context.Context):Promise<void>;