fix(ui): add disabled state and feedback to usage tips Add button

The Add button silently returned when no parameter or value was
provided, looking clickable but doing nothing. Keep it disabled until
both inputs are filled, validate the numeric value, surface save
failures via toast without clearing user input, and confirm additions
vs overwrites with success toasts. Includes translations for all
locales.

locales/zh-CN.json

@@ -1593,7 +1593,11 @@
                 "clipSkip": "Clip Skip",
                 "valuePlaceholder": "数值",
                 "add": "添加",
-                "invalidRange": "无效的范围格式。请使用 x.x-y.y"
+                "invalidRange": "无效的范围格式。请使用 x.x-y.y",
+                "invalidValue": "请输入有效的数值",
+                "saveFailed": "保存预设参数失败",
+                "added": "已添加预设参数",
+                "updated": "已更新预设参数"
             },
             "triggerWords": {
                 "label": "触发词",