refactor(mcp): switch to user-level config ~/.claude.json and remove project-level logic

- Read/write ~/.claude.json (preserve unknown fields) for mcpServers
- Remove settings.local.json and mcp.json handling
- Drop enableAllProjectMcpServers command and UI toggle
- Update types, Tauri APIs, and MCP panel to reflect new status fields
- Keep atomic write and command validation behaviors

src/i18n/locales/en.json

@@ -251,8 +251,7 @@
   },
   "mcp": {
     "title": "MCP Management",
-    "enableProject": "Enable project-level MCP servers",
-    "openFolder": "Open ~/.claude",
+    "userLevelPath": "User-level MCP path",
     "serverList": "Servers",
     "loading": "Loading...",
     "empty": "No MCP servers",
@@ -281,7 +280,6 @@
       "templateAdded": "Template added"
     },
     "error": {
-      "toggleFailed": "Failed to update toggle",
       "idRequired": "Please enter identifier",
       "commandRequired": "Please enter command",
       "saveFailed": "Save failed",

src/i18n/locales/zh.json

@@ -251,8 +251,7 @@
   },
   "mcp": {
     "title": "MCP 管理",
-    "enableProject": "启用项目级 MCP 服务器",
-    "openFolder": "打开 ~/.claude",
+    "userLevelPath": "用户级 MCP 配置路径",
     "serverList": "服务器列表",
     "loading": "加载中...",
     "empty": "暂无 MCP 服务器",
@@ -281,7 +280,6 @@
       "templateAdded": "已添加模板"
     },
     "error": {
-      "toggleFailed": "更新开关失败",
       "idRequired": "请填写标识",
       "commandRequired": "请填写命令",
       "saveFailed": "保存失败",