feat(02-02): add thread hooks, UI store, tab navigation, and thread list

- Create useThreads/useCandidates TanStack Query hooks
- Extend uiStore with candidate panel and resolve dialog state
- Add ThreadTabs component for gear/planning tab switching
- Add ThreadCard component with candidate count and price range chips
- Refactor index.tsx to tabbed HomePage with PlanningView
- Create placeholder thread detail route for navigation target

src/client/routes/threads/$threadId.tsx

@@ -0,0 +1,15 @@
+import { createFileRoute } from "@tanstack/react-router";
+
+export const Route = createFileRoute("/threads/$threadId")({
+  component: ThreadDetailPage,
+});
+
+function ThreadDetailPage() {
+  const { threadId } = Route.useParams();
+
+  return (
+    <div className="max-w-7xl mx-auto px-4 sm:px-6 lg:px-8 py-6">
+      <p>Thread {threadId} - detail page placeholder</p>
+    </div>
+  );
+}