fix(mcp): use browser-compatible platform detection for MCP presets

Replace Node.js process.platform check with navigator.userAgent-based
detection from @/lib/platform. The previous implementation using
process.platform failed in Tauri's browser environment, causing
Windows platform to always return false and not apply the required
'cmd /c' wrapper for npx commands.

This fix ensures that on Windows, MCP presets like sequential-thinking
correctly use 'cmd /c npx' format instead of direct 'npx', eliminating
the warning: "Windows requires 'cmd /c' wrapper to execute npx"

Changes:
- Import isWindows() from @/lib/platform instead of defining locally
- Remove incorrect process.platform-based detection
- Now properly detects Windows in browser/WebView environment

src/config/mcpPresets.ts

@@ -1,7 +1,25 @@
 import { McpServer, McpServerSpec } from "../types";
+import { isWindows } from "@/lib/platform";
 
 export type McpPreset = Omit<McpServer, "enabled" | "description">;
 
+// 创建跨平台 npx 命令配置
+// Windows 需要使用 cmd /c wrapper 来执行 npx.cmd
+// Mac/Linux 可以直接执行 npx
+const createNpxCommand = (packageName: string, extraArgs: string[] = []): { command: string; args: string[] } => {
+  if (isWindows()) {
+    return {
+      command: 'cmd',
+      args: ['/c', 'npx', ...extraArgs, packageName]
+    };
+  } else {
+    return {
+      command: 'npx',
+      args: [...extraArgs, packageName]
+    };
+  }
+};
+
 // 预设 MCP（逻辑简化版）：
 // - 仅包含最常用、可快速落地的 stdio 模式示例
 // - 不涉及分类/模板/测速等复杂逻辑，默认以 disabled 形式"回种"到 config.json
@@ -26,8 +44,7 @@ export const mcpPresets: McpPreset[] = [
     tags: ["stdio", "time", "utility"],
     server: {
       type: "stdio",
-      command: "npx",
-      args: ["-y", "@modelcontextprotocol/server-time"],
+      ...createNpxCommand("@modelcontextprotocol/server-time", ["-y"]),
     } as McpServerSpec,
     homepage: "https://github.com/modelcontextprotocol/servers",
     docs: "https://github.com/modelcontextprotocol/servers/tree/main/src/time",
@@ -38,8 +55,7 @@ export const mcpPresets: McpPreset[] = [
     tags: ["stdio", "memory", "graph"],
     server: {
       type: "stdio",
-      command: "npx",
-      args: ["-y", "@modelcontextprotocol/server-memory"],
+      ...createNpxCommand("@modelcontextprotocol/server-memory", ["-y"]),
     } as McpServerSpec,
     homepage: "https://github.com/modelcontextprotocol/servers",
     docs: "https://github.com/modelcontextprotocol/servers/tree/main/src/memory",
@@ -50,8 +66,7 @@ export const mcpPresets: McpPreset[] = [
     tags: ["stdio", "thinking", "reasoning"],
     server: {
       type: "stdio",
-      command: "npx",
-      args: ["-y", "@modelcontextprotocol/server-sequential-thinking"],
+      ...createNpxCommand("@modelcontextprotocol/server-sequential-thinking", ["-y"]),
     } as McpServerSpec,
     homepage: "https://github.com/modelcontextprotocol/servers",
     docs: "https://github.com/modelcontextprotocol/servers/tree/main/src/sequentialthinking",
@@ -62,8 +77,7 @@ export const mcpPresets: McpPreset[] = [
     tags: ["stdio", "docs", "search"],
     server: {
       type: "stdio",
-      command: "npx",
-      args: ["-y", "@upstash/context7-mcp"],
+      ...createNpxCommand("@upstash/context7-mcp", ["-y"]),
     } as McpServerSpec,
     homepage: "https://context7.com",
     docs: "https://github.com/upstash/context7/blob/master/README.md",