Move File Management link into the bottom tab bar

Replace the dashboard-only footer link with a "Files" item in the
persistent bottom tab bar (Home/Notes/Help/Settings) on every page, so
it's reachable the same way everywhere instead of only from the
dashboard.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

templates/notes_hub.html

@@ -282,6 +282,9 @@
         <a href="/settings" class="tab-item {% if active_tab == 'settings' %}active{% endif %}">
             <span class="tab-icon">{{ icons.icon('settings', 20) }}</span><span class="tab-label">Settings</span>
         </a>
+        <a href="/unsorted" class="tab-item {% if active_tab == 'files' %}active{% endif %}">
+            <span class="tab-icon">{{ icons.icon('folder', 20) }}</span><span class="tab-label">Files</span>
+        </a>
     </nav>
 
     <script>