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/zh.json

@@ -1479,6 +1479,8 @@
       "resetConfirm": "将菜单重置为默认设置？所有更改将丢失。",
       "buttonTextPlaceholder": "按钮文本",
       "customLabelsHint": "每种语言的按钮文本",
+      "moveUp": "上移",
+      "moveDown": "下移",
       "invalidUrl": "请为所有自定义按钮提供有效的URL（http:// 或 https://）"
     },
     "apps": {