feat(frontend): add MCP import dialog for v3.7.0

Implement import functionality to migrate MCP servers from existing configs:

**New Component:**
- src/components/mcp/McpImportDialog.tsx: Import dialog with card-based source selection

**Features:**
- Import from Claude (~/.claude/claude.json or settings.json)
- Import from Codex (~/.codex/config.toml)
- Import from Gemini (config file)
- Card-based UI with icons and descriptions
- Loading states with spinner animation
- Auto-refresh after successful import

**Integration:**
- Add import button to UnifiedMcpPanel header
- Handle import completion with refetch
- Toast notifications for success/info/error cases

**I18n:**
- Add mcp.unifiedPanel.import namespace (zh/en)
- Import button, dialog title, descriptions
- Success/error messages with count interpolation

**UX:**
- Smart disable: other sources disabled during import
- Clear feedback: count of imported servers
- Friendly messages: "No servers found" when empty

TypeScript type check passes ✅

src/i18n/locales/zh.json

@@ -455,6 +455,16 @@
         "claude": "Claude",
         "codex": "Codex",
         "gemini": "Gemini"
+      },
+      "import": {
+        "title": "导入 MCP 服务器",
+        "button": "导入",
+        "description": "从已有的应用配置文件中导入 MCP 服务器。导入的服务器将自动启用对应的应用。",
+        "fromClaudeDesc": "从 ~/.claude/claude.json 或 ~/.claude/settings.json 导入 MCP 服务器",
+        "fromCodexDesc": "从 ~/.codex/config.toml 导入 MCP 服务器",
+        "fromGeminiDesc": "从 Gemini 配置文件导入 MCP 服务器",
+        "success": "成功导入 {{count}} 个服务器",
+        "noServersFound": "未找到可导入的服务器"
       }
     },
     "userLevelPath": "用户级 MCP 配置路径",