feat(17-01): add WriteTrackTagsByPath and ImageFilePicker backend methods

- WriteTrackTagsByPath resolves filePath to trackID via GetAudioFileByPath
- ImageFilePicker opens native file dialog filtered to JPEG/PNG
- Added Wails TypeScript bindings for both new methods

frontend/wailsjs/go/frontendutil/FrontendUtil.d.ts

@@ -4,6 +4,8 @@ import {context} from '../models';
 
 export function DirectoryPicker():Promise<string>;
 
+export function ImageFilePicker():Promise<string>;
+
 export function PlaylistFilePicker():Promise<Array<string>>;
 
 export function SetContext(arg1:context.Context):Promise<void>;