Clean up backend and web-player leftovers

Remove dead scaffold/config cruft and stale references left over from
recent refactors: dotnet's WebApi.http template file, the AppSettings
PascalCase/Dockerfile workaround (renamed to appsettings.json to match
convention), empty directories left behind by the auth-route and
folder-structure moves, a stale ESLint ignore, and the now-fully-applied
frontend refactor plan doc.

web-player/eslint.config.js

@@ -36,12 +36,6 @@ export default ts.config(
 		}
 	},
 	{
-		ignores: [
-			'build/',
-			'.svelte-kit/',
-			'static/',
-			'src/lib/api/schema.d.ts',
-			'design_handoff_musify_player/'
-		]
+		ignores: ['build/', '.svelte-kit/', 'static/', 'src/lib/api/schema.d.ts']
 	}
 );