feat(deepfield): 렌더 모드 판정(TDD) + useFieldMode 훅

app/components/deepfield/useFieldMode.ts

@@ -0,0 +1,29 @@
+'use client';
+
+import { useEffect, useState } from 'react';
+import { decideFieldMode, type FieldMode } from '@/lib/deepfield-mode';
+
+function detectWebGL(): boolean {
+  try {
+    const canvas = document.createElement('canvas');
+    return Boolean(canvas.getContext('webgl2') ?? canvas.getContext('webgl'));
+  } catch {
+    return false;
+  }
+}
+
+/** SSR/첫 페인트는 'static'으로 시작 — 클라이언트에서 승격 (hydration 불일치 방지) */
+export function useFieldMode(): FieldMode {
+  const [mode, setMode] = useState<FieldMode>('static');
+  useEffect(() => {
+    setMode(
+      decideFieldMode({
+        reducedMotion: window.matchMedia('(prefers-reduced-motion: reduce)').matches,
+        webglSupported: detectWebGL(),
+        hardwareConcurrency: navigator.hardwareConcurrency ?? 0,
+        viewportWidth: window.innerWidth,
+      }),
+    );
+  }, []);
+  return mode;
+}