feat(chess): add rule-toggle UI with compatibility warnings (P3.11)

packages/chess/src/app/App.tsx

@@ -1,5 +1,6 @@
 import { Routes, Route } from 'react-router-dom'
 import { GameView } from '../ui/GameView'
+import { RulesView } from '../ui/RulesView'
 
 export function App() {
   return (
@@ -7,7 +8,7 @@ export function App() {
       <Routes>
         <Route path="/" element={<Home />} />
         <Route path="/game" element={<GameView />} />
-        <Route path="/rules" element={<Rules />} />
+        <Route path="/rules" element={<RulesView />} />
         <Route path="/save" element={<Save />} />
       </Routes>
     </div>
@@ -22,14 +23,6 @@ function Home() {
   )
 }
 
-function Rules() {
-  return (
-    <main data-testid="page-rules">
-      <h1>Rules</h1>
-    </main>
-  )
-}
-
 function Save() {
   return (
     <main data-testid="page-save">

packages/chess/src/ui/RulesView.tsx

@@ -0,0 +1,104 @@
+import { useState, useMemo } from 'react';
+import { useNavigate } from 'react-router-dom';
+import { PRESET_REGISTRY } from '../presets/index.js';
+
+export function RulesView({ isGameActive }: { isGameActive?: boolean }) {
+  const navigate = useNavigate();
+  const [selected, setSelected] = useState<Set<string>>(new Set());
+
+  const presets = PRESET_REGISTRY.getAll();
+
+  const hasIncompatibilities = useMemo(() => {
+    for (const a of selected) {
+      const aDef = presets.find((p) => p.id === a);
+      if (!aDef) continue;
+      for (const b of selected) {
+        if (a === b) continue;
+        if (aDef.incompatibleWith.includes(b)) return true;
+      }
+    }
+    return false;
+  }, [selected, presets]);
+
+  const togglePreset = (id: string) => {
+    if (isGameActive) return;
+    setSelected((prev) => {
+      const next = new Set(prev);
+      if (next.has(id)) {
+        next.delete(id);
+      } else {
+        next.add(id);
+      }
+      return next;
+    });
+  };
+
+  const handleApply = () => {
+    setSelected(new Set());
+    navigate('/game');
+  };
+
+  return (
+    <div className="p-6 max-w-3xl mx-auto space-y-6" data-testid="page-rules">
+      <h1 className="text-3xl font-bold">Preset Rules</h1>
+
+      {isGameActive && (
+        <div className="bg-gray-100 text-gray-700 p-4 rounded-md">
+          Rules can only be changed between games
+        </div>
+      )}
+
+      {hasIncompatibilities && (
+        <div data-testid="compat-warning" className="bg-amber-100 text-amber-800 p-4 rounded-md font-semibold">
+          Warning: Some selected rules are mutually incompatible.
+        </div>
+      )}
+
+      <div className="space-y-4">
+        {presets.map((preset) => (
+          <div
+            key={preset.id}
+            data-preset={preset.id}
+            className={`border rounded-lg p-4 flex items-center justify-between transition-colors ${
+              isGameActive ? 'opacity-50 grayscale' : 'hover:border-blue-400'
+            }`}
+          >
+            <div className="pr-4">
+              <h3 className="text-lg font-semibold">{preset.name}</h3>
+              <p className="text-sm text-gray-600 mt-1">{preset.description}</p>
+            </div>
+            <button
+              type="button"
+              data-role="toggle"
+              disabled={isGameActive}
+              onClick={() => togglePreset(preset.id)}
+              className={`relative inline-flex h-6 w-11 flex-shrink-0 cursor-pointer rounded-full border-2 border-transparent transition-colors duration-200 ease-in-out focus:outline-none focus:ring-2 focus:ring-blue-600 focus:ring-offset-2 ${
+                selected.has(preset.id) ? 'bg-blue-600' : 'bg-gray-200'
+              } ${isGameActive ? 'cursor-not-allowed' : ''}`}
+              role="switch"
+              aria-checked={selected.has(preset.id)}
+            >
+              <span
+                aria-hidden="true"
+                className={`pointer-events-none inline-block h-5 w-5 transform rounded-full bg-white shadow ring-0 transition duration-200 ease-in-out ${
+                  selected.has(preset.id) ? 'translate-x-5' : 'translate-x-0'
+                }`}
+              />
+            </button>
+          </div>
+        ))}
+      </div>
+
+      <div className="pt-6">
+        <button
+          type="button"
+          data-action="start-new-game"
+          onClick={handleApply}
+          className="w-full bg-blue-600 text-white rounded-lg py-3 px-4 font-semibold hover:bg-blue-700 transition-colors"
+        >
+          Apply and start new game
+        </button>
+      </div>
+    </div>
+  );
+}