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/components/ThreadTabs.tsx

@@ -0,0 +1,33 @@
+interface ThreadTabsProps {
+  active: "gear" | "planning";
+  onChange: (tab: "gear" | "planning") => void;
+}
+
+const tabs = [
+  { key: "gear" as const, label: "My Gear" },
+  { key: "planning" as const, label: "Planning" },
+];
+
+export function ThreadTabs({ active, onChange }: ThreadTabsProps) {
+  return (
+    <div className="flex border-b border-gray-200">
+      {tabs.map((tab) => (
+        <button
+          key={tab.key}
+          type="button"
+          onClick={() => onChange(tab.key)}
+          className={`px-4 py-2.5 text-sm font-medium transition-colors relative ${
+            active === tab.key
+              ? "text-blue-600"
+              : "text-gray-500 hover:text-gray-700"
+          }`}
+        >
+          {tab.label}
+          {active === tab.key && (
+            <span className="absolute bottom-0 left-0 right-0 h-0.5 bg-blue-600 rounded-t" />
+          )}
+        </button>
+      ))}
+    </div>
+  );
+}