fix: resolve test pollution from freeze_saves and fix os_listener toggle

- Add unfreeze_saves() to base_store.py and call it in e2e cleanup.
  The backup restore flow calls freeze_saves() which sets a module-level
  flag that silently disables all store _save() calls. Without reset,
  this poisoned all subsequent persistence tests (9 failures).
- Fix os_listener toggle to use toggle-switch/toggle-slider CSS classes
  instead of nonexistent switch/slider classes (was showing plain checkbox).
- Add mandatory test run to CLAUDE.md pre-commit checks.

All 341 tests now pass.

server/src/wled_controller/templates/modals/css-editor.html

@@ -381,9 +381,9 @@
                             <button type="button" class="hint-toggle" onclick="toggleHint(this)" title="?" data-i18n-aria-label="aria.hint">?</button>
                         </div>
                         <small class="input-hint" style="display:none" data-i18n="color_strip.notification.os_listener.hint">When enabled, this source automatically fires when a desktop notification appears (Windows toast / Linux D-Bus). Requires the app to have notification access permission.</small>
-                        <label class="switch">
+                        <label class="toggle-switch">
                             <input type="checkbox" id="css-editor-notification-os-listener">
-                            <span class="slider"></span>
+                            <span class="toggle-slider"></span>
                         </label>
                     </div>