feat(admin): show auth source badge and hide password reset for OIDC users

The admin user list now displays an OIDC/Local badge per user and
hides the password reset button for OIDC-provisioned accounts.

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

static/admin.html

@@ -92,13 +92,14 @@
               <tr>
                 <th>User</th>
                 <th>Role</th>
+                <th>Auth</th>
                 <th>Status</th>
                 <th>Storage</th>
                 <th>Last Login</th>
                 <th>Actions</th>
               </tr>
             </thead>
-            <tbody id="users-tbody"><tr><td colspan="6" class="table-loading-cell"><i class="fas fa-spinner fa-spin"></i> Loading users…</td></tr></tbody>
+            <tbody id="users-tbody"><tr><td colspan="7" class="table-loading-cell"><i class="fas fa-spinner fa-spin"></i> Loading users…</td></tr></tbody>
           </table>
         </div>
         <div class="pagination">