feat(skill): add three-state upload progress tooltip

Replace simple uploading/success indicator with a full three-state
tooltip (uploading, success, partial_error) that overlays the DropTip
position. Add upload slice to skill editor store and wire progress
tracking into file/folder upload operations.

web/i18n/en-US/workflow.json

@@ -1141,7 +1141,12 @@
   "skillSidebar.unsavedChanges.confirmClose": "Discard",
   "skillSidebar.unsavedChanges.content": "You have unsaved changes. Do you want to discard them?",
   "skillSidebar.unsavedChanges.title": "Unsaved changes",
+  "skillSidebar.uploadPartialError": "Some uploads failed",
+  "skillSidebar.uploadPartialErrorDetail": "{{failed}} of {{total}} uploads failed.",
+  "skillSidebar.uploadSuccess": "Upload successful",
+  "skillSidebar.uploadSuccessDetail": "{{uploaded}} of {{total}} uploads complete",
   "skillSidebar.uploading": "Uploading…",
+  "skillSidebar.uploadingItems": "Uploading {{uploaded}} of {{total}} items",
   "subGraphModal.canvasPlaceholder": "Click to configure the internal structure",
   "subGraphModal.defaultValueHint": "Returns the value below",
   "subGraphModal.internalStructure": "Internal structure",

web/i18n/zh-Hans/workflow.json

@@ -1131,7 +1131,12 @@
   "skillSidebar.unsavedChanges.confirmClose": "放弃",
   "skillSidebar.unsavedChanges.content": "您有未保存的更改，是否放弃？",
   "skillSidebar.unsavedChanges.title": "未保存的更改",
+  "skillSidebar.uploadPartialError": "部分上传失败",
+  "skillSidebar.uploadPartialErrorDetail": "{{total}} 个文件中有 {{failed}} 个上传失败。",
+  "skillSidebar.uploadSuccess": "上传成功",
+  "skillSidebar.uploadSuccessDetail": "{{total}} 个文件中已完成 {{uploaded}} 个",
   "skillSidebar.uploading": "上传中…",
+  "skillSidebar.uploadingItems": "正在上传 {{total}} 个项目中的第 {{uploaded}} 个",
   "subGraphModal.canvasPlaceholder": "点击配置内部结构",
   "subGraphModal.defaultValueHint": "返回以下值",
   "subGraphModal.internalStructure": "内部结构",