chore(core/frontend): remove dead codex-era exact-* code (§6)

Removed unused codex/iframe-era modules (confirmed no live imports; public/exact/*.html design baselines kept):
- routes/exact-document.tsx, routes/exact-html.ts (~1.6MB generated), routes/exact-dashboard.tsx, routes/exact-pages/ (24 files)
- exact-pages.css + its main.tsx import; index.ts ExactDashboardApp re-export
App.tsx uses the real Dashboard; nothing referenced the removed cluster.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

core/frontend/src/main.tsx

@@ -2,7 +2,6 @@ import { createRoot } from "react-dom/client";
 import { App } from "./App";
 import "./styles.css";
 import "./design-restraint.css";
-import "./exact-pages.css";
 import "./account-page.css";
 import "./product-detail-page.css";
 import "./team-page.css";