feat(inbox): PendingBanner with v0.2 copy

Task 24 of the slice plan. Subscribes to pendingCount in the
store and renders '🟡 Inkling이 정리하는 중: N건' when count > 0.
Hidden when zero so the layout doesn't reserve space.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/renderer/inbox/components/PendingBanner.tsx

@@ -1,2 +1,12 @@
 import React from 'react';
-export function PendingBanner() { return null; }
+import { useInbox } from '../store.js';
+
+export function PendingBanner(): React.ReactElement | null {
+  const count = useInbox((s) => s.pendingCount);
+  if (count === 0) return null;
+  return (
+    <div className="banner info">
+      <span>🟡 Inkling이 정리하는 중: <b>{count}</b>건</span>
+    </div>
+  );
+}