Offline access: also save what the app needs to start

The app asks who is signed in, the accounts and the folders once, when it
loads — before the service worker exists if offline access was just turned
on. Without a reload those were never saved, so going offline ended on
"Can't reach the server". Pre-loading now fetches them too.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/src/lib/offlinePrefetch.ts

@@ -37,6 +37,18 @@ async function fetchOnce(url: string): Promise<string | null> {
 
 async function run(): Promise<void> {
   if (!(await offlineReady()) || isOffline()) return;
+  // What the app asks for when it starts (who is signed in, accounts, folders…).
+  // The page fetched these once on load — possibly before the service worker
+  // was there to save them — so fetch them again now, or the app could not
+  // start offline at all.
+  await Promise.allSettled([
+    api.me(),
+    api.accounts(),
+    api.mailboxes(),
+    api.quota(),
+    api.savedSearches(),
+    api.uiManifest(),
+  ]);
   const settings = await api.settings();
   const order = settings.thread_order ?? "asc";
   // The list as the app shows it (newest first is the default), plus the other