feat: landing page + logo, dev-mode banner + sync cap, non-blocking sync with progress splash

frontend/src/api/client.js

@@ -7,13 +7,21 @@ api.interceptors.response.use(
   (r) => r,
   (err) => {
     if (err.response?.status === 401) {
-      // Not signed in — kick off the Google login flow.
-      window.location.href = '/api/v1/auth/login?returnUrl=/';
+      // Not signed in. Send the user to the public landing page (unless already
+      // there) so they can read the features and choose to log in.
+      if (window.location.pathname !== '/') window.location.href = '/';
     }
     return Promise.reject(err);
   }
 );
 
+// Top-level navigation that starts the Google flow and returns to the app.
+export const LOGIN_URL = '/api/v1/auth/login?returnUrl=/app';
+
+export const AppApi = {
+  info: () => api.get('/app/info').then((r) => r.data)
+};
+
 export const AuthApi = {
   me: () => api.get('/auth/me').then((r) => r.data),
   logout: () => api.post('/auth/logout')