feat(renderer): useMenuAction hook (native menu IPC -> command store)

- bridge between main-process menu events and the command dispatcher
- optional transform: convert raw IPC payload to command args
- extends ipc.ts with ipc.menu.on() helper
- TDD: 5 unit tests covering subscription, payload transform, no-op, unmount

src/renderer/hooks/use-menu-action.ts

@@ -0,0 +1,29 @@
+import { useEffect } from 'react';
+import { ipc } from '@/lib/ipc';
+import { useCommandStore } from '@/stores/command-store';
+import type { CommandId } from '@/stores/command-store';
+
+type Transform<Args = unknown> = (...payload: unknown[]) => Args;
+
+/**
+ * Bridge a native-menu IPC channel to a command-store dispatch.
+ *
+ * When the main process sends `channel` (e.g. `'file-save'`), the optional
+ * `transform` converts the payload to the command's args, then the command
+ * `commandId` is dispatched through the command store.
+ *
+ * The hook cleans up its IPC subscription on unmount.
+ */
+export function useMenuAction<Args = unknown>(
+  channel: string,
+  commandId: CommandId,
+  transform?: Transform<Args>
+): void {
+  useEffect(() => {
+    const unsubscribe = ipc.menu.on(channel, (...payload: unknown[]) => {
+      const args = transform ? transform(...payload) : (payload[0] as Args);
+      useCommandStore.getState().dispatch(commandId, args);
+    });
+    return unsubscribe;
+  }, [channel, commandId, transform]);
+}