feat: 新增 HTTP MCP Server，让 AI Agent 接入选菜

新增 packages/mcp，基于 Streamable HTTP 暴露菜谱库能力，复用 packages/cook 的选菜算法：recommend_recipes 按现有食材推荐，search_recipes 条件检索，check_incompatible 食材相克，get_recipe 菜谱详情。容器内与 nginx 共存，映射 2230 端口供 Agent 连接。

package.json

@@ -20,6 +20,8 @@
     "fixtures": "tsx scripts/gen-fixtures.ts",
     "dev": "pnpm -C apps/web run dev",
     "dev:pwa": "pnpm -C apps/web run dev:pwa",
+    "mcp": "pnpm -C packages/mcp run dev",
+    "mcp:build": "pnpm -C packages/mcp run build",
     "docs:dev": "pnpm -C docs run docs:dev",
     "docs:build": "pnpm -C docs run docs:build",
     "generate": "pnpm -C apps/web run generate && tsx scripts/copy-web-output.ts",