feat: add button reordering within rows and replace modal with inline add panel

- Add up/down arrow buttons to reorder buttons within rows (builtin + custom)
- Replace AddButtonDialog modal (bg-black/50 overlay) with inline expandable panel
- Add moveUp/moveDown i18n keys for all locales (en/ru/zh/fa)
- Add aria-labels for accessibility on reorder buttons

src/locales/en.json

@@ -1779,6 +1779,8 @@
       "resetConfirm": "Reset menu layout to defaults?",
       "buttonTextPlaceholder": "Custom button text",
       "customLabelsHint": "Empty = default label",
+      "moveUp": "Move up",
+      "moveDown": "Move down",
       "invalidUrl": "Please provide a valid URL (http:// or https://) for all custom buttons"
     },
     "apps": {