feat: add login button to header and conditional edit UI

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/client/routes/__root.tsx

@@ -13,6 +13,7 @@ import { ItemForm } from "../components/ItemForm";
 import { OnboardingWizard } from "../components/OnboardingWizard";
 import { SlideOutPanel } from "../components/SlideOutPanel";
 import { TotalsBar } from "../components/TotalsBar";
+import { useAuth } from "../hooks/useAuth";
 import { useDeleteCandidate } from "../hooks/useCandidates";
 import { useOnboardingComplete } from "../hooks/useSettings";
 import { useResolveThread, useThread } from "../hooks/useThreads";
@@ -24,6 +25,8 @@ export const Route = createRootRoute({
 
 function RootLayout() {
 	const navigate = useNavigate();
+	const { data: auth } = useAuth();
+	const isAuthenticated = !!auth?.user;
 
 	// Item panel state
 	const panelMode = useUIStore((s) => s.panelMode);
@@ -175,7 +178,7 @@ function RootLayout() {
 			)}
 
 			{/* Floating Add Button - only on collection gear tab */}
-			{showFab && (
+			{showFab && isAuthenticated && (
 				<button
 					type="button"
 					onClick={openAddPanel}