chore(frontend): slim admin.ts, remove dead library.ts

- Remove dead functions from admin.ts: loadSystemStats, renderSystemStats,
  triggerLibraryScan, triggerQuickScan, all WebSocket functions
- Remove library.ts (695 lines of innerHTML string-building replaced by
  HTMX server-rendered partials)
- Remove library import from main.ts

web/src/main.ts

@@ -20,7 +20,6 @@ import "./dom";
 import "./events";
 import "./header";
 import "./index";
-import "./library";
 import "./library-switcher";
 import "./linking";
 import "./login";