Add React UI with Vite

Dashboard, agents, goals, issues, and projects pages with sidebar
navigation. API client layer, custom hooks, and shared layout
components. Built with Vite and TypeScript.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

ui/src/components/Sidebar.tsx

@@ -0,0 +1,37 @@
+import { NavLink } from "react-router-dom";
+import { cn } from "../lib/utils";
+
+const links = [
+  { to: "/", label: "Dashboard" },
+  { to: "/agents", label: "Agents" },
+  { to: "/projects", label: "Projects" },
+  { to: "/issues", label: "Issues" },
+  { to: "/goals", label: "Goals" },
+];
+
+export function Sidebar() {
+  return (
+    <aside className="w-56 border-r border-gray-200 bg-white p-4 flex flex-col gap-1">
+      <h1 className="text-lg font-bold mb-6 px-3">Paperclip</h1>
+      <nav className="flex flex-col gap-1">
+        {links.map((link) => (
+          <NavLink
+            key={link.to}
+            to={link.to}
+            end={link.to === "/"}
+            className={({ isActive }) =>
+              cn(
+                "px-3 py-2 rounded-md text-sm font-medium transition-colors",
+                isActive
+                  ? "bg-gray-100 text-gray-900"
+                  : "text-gray-600 hover:bg-gray-50 hover:text-gray-900"
+              )
+            }
+          >
+            {link.label}
+          </NavLink>
+        ))}
+      </nav>
+    </aside>
+  );
+}