feat(mobile): add Profiles button to mobile bottom navigation (#265)

Adds a Profiles button as the last item in the mobile bottom nav bar,
making the Profiles panel reachable on mobile without opening the sidebar.

Fixes from original PR:
- Uses mobileSwitchPanel('profiles') not the broken two-call approach
- data-panel='profiles' attribute present for active-highlight state
- SVG 20x20 stroke-width 1.5 matching all other mobile nav icons
- Placed last (Chat → Tasks → Skills → Memory → Spaces → Profiles)
- 3 new tests in test_mobile_layout.py covering presence, handler, and order

Tests: 700 passed (up from 697)

Co-authored-by: @gabogabucho

Co-authored-by: Nathan Esquenazi <nesquena@gmail.com>

static/index.html

@@ -481,6 +481,10 @@
     <svg width="20" height="20" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.5"><path d="M2 4h8l2 2h10v14H2z"/></svg>
     <span data-i18n="tab_workspaces">Spaces</span>
   </button>
+  <button class="mobile-nav-btn" data-panel="profiles" onclick="mobileSwitchPanel('profiles')">
+    <svg width="20" height="20" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true"><path d="M20 21v-2a4 4 0 0 0-4-4H8a4 4 0 0 0-4 4v2"/><circle cx="12" cy="7" r="4"/></svg>
+    <span data-i18n="tab_profiles">Profiles</span>
+  </button>
 </nav>
 <div class="toast" id="toast"></div>
 <script src="/static/i18n.js"></script>