Add UserButton to SideNav, refactor NavButton into TeamsButton

- Create UserButton component at bottom of SideNav with Settings, Language,
  Theme, Admin, and Logout menu items
- Move Settings/Logout/Admin/Docs/Support out of NavButton into UserButton
- Remove LanguageButton and ThemeButton from SideNav bottom
- Refactor NavButton into TeamsButton with simplified team switching
- Simplify WebsiteNav and move TeamsButton to App top bar

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/app/(main)/App.tsx

@@ -5,6 +5,7 @@ import { useEffect } from 'react';
 import { MobileNav } from '@/app/(main)/MobileNav';
 import { SideNav } from '@/app/(main)/SideNav';
 import { useConfig, useLoginQuery, useNavigation } from '@/components/hooks';
+import { TeamsButton } from '@/components/input/TeamsButton';
 import { LAST_TEAM_CONFIG } from '@/lib/constants';
 import { removeItem, setItem } from '@/lib/storage';
 import { UpdateNotice } from './UpdateNotice';
@@ -50,6 +51,18 @@ export function App({ children }) {
         <SideNav />
       </Column>
       <Column overflowX="hidden" position="relative">
+        <Row
+          position="sticky"
+          top="0"
+          alignItems="center"
+          justifyContent="space-between"
+          paddingY="2"
+          zIndex={100}
+        >
+          <Row backgroundColor="surface-raised">
+            <TeamsButton />
+          </Row>
+        </Row>
         <Column alignItems="center">{children}</Column>
       </Column>
       <UpdateNotice user={user} config={config} />