design: Sign out is a POST form in the mockups, tinted like the links

Owner's instruction (2026-10-09): in the kit Sign out had no hover tint and
stood out among Account and Help. The cause was in the design, not in the
implementation: the mockups drew Sign out as a link, the panel signs out
with a POST, and Bulma tints only a.navbar-item.

  - build.py: Sign out is a form with a submit button carrying navbar-item,
    as the real shell has to write it; all pages rebuilt.
  - theme.css: the form stretches the button across the menu and the button
    is handed Bulma's own hover / focus / active variables, so it answers
    like the entries above it. No width, no colour of its own.

check.py: 32 screens, 48 sp- classes, 0 violation(s); outlines.json unchanged.

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

docs/assets/panel-redesign/panel/backup.html

@@ -54,7 +54,7 @@
             <a class="navbar-item" href="account.html"><i class="ti ti-key"></i>Account</a>
             <a class="navbar-item" href="help.html"><i class="ti ti-help"></i>Help</a>
             <hr class="navbar-divider">
-            <a class="navbar-item" href="login.html"><i class="ti ti-logout"></i>Sign out</a>
+            <form method="post" action="login.html"><button type="submit" class="navbar-item"><i class="ti ti-logout"></i>Sign out</button></form>
           </div>
         </div>
       </div>