fix: close form tag before Restore Database section to fix nested form bug

The Restore Calibre Database form (action=admin.restore_calibre_db) was
nested inside the outer DB Configuration form (action=admin.db_configuration).
HTML doesn't allow nested forms; browsers drop the inner <form> tag during
parsing but keep its children (the CSRF input and submit button) as part of
the outer form. As a result, clicking "Restore Calibre Database (Last
Resort)" always submitted the outer db_configuration form instead - silently
saving the basic config fields and doing nothing else, with no error and no
indication anything was wrong.

Fix: close the outer form right after the Save/Cancel row, before the
Restore section begins, instead of wrapping the whole page in one form. The
settings-container div still visually wraps both sections; only the <form>
boundary changes. No other markup, styling, or route logic touched.

Verified by hand: without the fix, both DevTools Network capture and
container logs show every click POSTing to /admin/dbconfig with only
config_calibre_dir/config_calibre_split_dir fields - /admin/restore_calibre_db
is never hit. With the fix (tested by calling the intended endpoint
directly), the restore runs correctly and rebuilds metadata.db from the
library's OPF files.

Author: luisalduucin

cps/templates/config_db.html

@@ -110,6 +110,7 @@ <h2 style="margin-bottom: 4rem;">{{_("Split Library Functionality")}}</h2>
       <div id="db_submit" name="submit" class="btn btn-default">{{_('Save')}}</div>
       <a href="{{ url_for('admin.admin') }}" id="config_back" class="btn btn-default">{{_('Cancel')}}</a>
     </div>
+  </form>
 
     <hr style="margin: 3rem 0;">
 
@@ -122,7 +123,6 @@ <h2>{{ _('Last Resort: Restore Calibre Database (experimental)') }}</h2>
       </form>
     </div>
     </div>
-  </form>
 </div>
 {% endblock %}
 {% block modal %}