Fix review findings and remove Uncategorized from sidebar

Backend: cache Google access tokens (drop dead access_token_expires_at,
migration 0007), handle MeTube cleared/canceled events by URL, return
email from /auth/status only when authenticated, move Google base URLs
into settings, run container as non-root.

Frontend: include local feed filters in the query key, remove dead
Saved page and unused assets, drop stale CategoryNav props and classes,
send Content-Type only with a body, remove Uncategorized from sidebar.

frontend/src/components/AppShell.tsx

@@ -41,7 +41,6 @@ function Sidebar({ close }: { close: () => void }) {
   const categories = categoriesQuery.data ?? []
   const links = [
     { to: '/', icon: 'home' as const, text: 'Все видео', end: true },
-    { to: '/uncategorized', icon: 'folder' as const, text: 'Без категории' },
     { to: '/local', icon: 'server' as const, text: 'На сервере' },
   ]
   return <nav className="sidebar-nav" aria-label="Основная навигация">