feat: add cs-dust2 React case with two model takes + react kind support

New case cs-dust2 (kind:react): a from-scratch React + three.js 5v5 Dust2 FPS.
Two takes registered: Claude Fable 5 / Claude Code / High (with a hand fix for a
64Hz fixed-step firing bug on high-refresh displays) and Claude Opus 4.8 /
Claude Code / Max (dust2-arena, one-shot). React cases commit source only; the
single file is built from source at deploy time. validate-data.ts now accepts a
React project directory as the declared artifact. AGENTS.md rewritten
English-only with React-case, bare-harness (no skills/plugins) and
artifact-anonymity rules.

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

outputs/claude-opus-4-8/claude-code-max/dust2-arena/src/main.tsx

@@ -0,0 +1,7 @@
+import { createRoot } from 'react-dom/client';
+import { App } from './App';
+import './styles.css';
+
+// No StrictMode: the game owns an imperative three.js loop with manual setup /
+// teardown, and double-invoked effects would spin up two render loops.
+createRoot(document.getElementById('root')!).render(<App />);