feat(links): align the friends page layout and submit UI

- assemble the friends template with page header, search cover, content position, widget zones and comments
- render the three page title styles and the tabbed search cover
- restore card, category nav and submit modal markup for the friends page
- add page content style support to the page editor
- port the linked card, category nav and submit modal styles to the mobile and desktop breakpoints

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

tests/widget-system/auth-source-contract.test.cjs

@@ -294,7 +294,7 @@ test('the top-nav user popover reproduces the reference quick-login block', () =
   // Callers append the block verbatim — no hand-rolled separator or wrapper.
   assert.match(header, /render_social_buttons\(__\('快速登录', 'jio'\)\)/);
   assert.doesNotMatch(header, /social-separator|social_loginbar/);
-  assert.match(links, /render_social_buttons\(__\('使用以下方式快速登录', 'jio'\)\)/);
+  assert.match(links, /render_social_buttons\(\)/);
   assert.doesNotMatch(links, /social_loginbar/);
 
   // The retired .social-login-divider / .oauth-row / .oauth-btn markup and its