frontend: add LoginGate, wire session into App, add logout link

frontend/src/App.tsx

@@ -5,6 +5,7 @@ import { Dashboard } from "./pages/Dashboard";
 import { Plan } from "./pages/Plan";
 import { Profile } from "./pages/Profile";
 import { ReviewQueue } from "./pages/ReviewQueue";
+import type { SessionInfo } from "./types/api";
 
 const TABS = [
   { key: "activities", label: "Activities", icon: "☰", Component: ReviewQueue },
@@ -14,7 +15,7 @@ const TABS = [
 
 type TabKey = (typeof TABS)[number]["key"];
 
-function App() {
+function App({ session }: { session: SessionInfo }) {
   const [tab, setTab] = useState<TabKey>("activities");
   // Profile isn't a tab: it's reached via the profile name in the top-right
   // corner instead, since (for now, single-profile) it's account settings,
@@ -47,13 +48,18 @@ function App() {
             </button>
           ))}
         </nav>
-        <button
-          type="button"
-          className={showProfile ? "profile-name active" : "profile-name"}
-          onClick={() => setShowProfile(true)}
-        >
-          {profileName ?? "Profile"}
-        </button>
+        <div className="header-actions">
+          <button
+            type="button"
+            className={showProfile ? "profile-name active" : "profile-name"}
+            onClick={() => setShowProfile(true)}
+          >
+            {profileName ?? "Profile"}
+          </button>
+          <a className="logout-link" href="/api/session/logout" title={session.email}>
+            Log out
+          </a>
+        </div>
       </header>
       <main>{showProfile ? <Profile onSaved={(p) => setProfileName(p.Name)} /> : <Active />}</main>
     </div>