feat(renderer): Zen mode (Esc exits, hides chrome)

src/renderer/hooks/use-zen-mode.ts

@@ -0,0 +1,22 @@
+import { useEffect } from 'react';
+import { useAppStore } from '@/stores/app-store';
+
+/**
+ * Mounts a global keydown listener that exits zen mode when the user
+ * presses Escape. Should be called once at the App root.
+ */
+export function useZenMode() {
+  const zenMode = useAppStore((s) => s.zenMode);
+  const setZenMode = useAppStore((s) => s.setZenMode);
+
+  useEffect(() => {
+    if (!zenMode) return;
+    const handler = (e: KeyboardEvent) => {
+      if (e.key === 'Escape') {
+        setZenMode(false);
+      }
+    };
+    window.addEventListener('keydown', handler);
+    return () => window.removeEventListener('keydown', handler);
+  }, [zenMode, setZenMode]);
+}