fix(13-02): resolve phantom playlist tracks using M3U8 paths after scan

- Add ScanHooks callback struct to library package (follows RemovalHooks pattern)
- Move phantom resolution from library to playlist service via hook
- New ResolvePhantomTracksAfterScan reads M3U8 files and resolves paths
  against current audio_files using multi-root resolution
- Handles pre-existing phantoms (match by M3U8 position) and new ones
  (match by phantom_file_path)
- Delete old resolvePhantomTracks method that required phantom_file_path
- Wire ScanHooks in app.go OnStartup

frontend/wailsjs/go/library/Library.d.ts

@@ -76,4 +76,6 @@ export function SetRemovalHooks(arg1:library.RemovalHooks):Promise<void>;
 
 export function SetRescanHooks(arg1:library.RescanHooks):Promise<void>;
 
+export function SetScanHooks(arg1:library.ScanHooks):Promise<void>;
+
 export function SoftScanAllLibraries():Promise<void>;

frontend/wailsjs/go/library/Library.js

@@ -146,6 +146,10 @@ export function SetRescanHooks(arg1) {
   return window['go']['library']['Library']['SetRescanHooks'](arg1);
 }
 
+export function SetScanHooks(arg1) {
+  return window['go']['library']['Library']['SetScanHooks'](arg1);
+}
+
 export function SoftScanAllLibraries() {
   return window['go']['library']['Library']['SoftScanAllLibraries']();
 }