feat: add plugin-mcp-server with MCPServerRuntime and MCPServerPlugin

Implements the MCP Runtime Server plugin that bridges ObjectStack kernel
services to the Model Context Protocol (MCP). Features:
- Tool bridge: all ToolRegistry tools → MCP tools
- Resource bridge: MetadataService → object schemas, DataEngine → records
- Prompt bridge: Agent definitions → MCP prompts
- StdioServerTransport for local AI client integration
- Environment variable configuration (MCP_SERVER_ENABLED, MCP_SERVER_NAME)

Agent-Logs-Url: https://github.com/objectstack-ai/framework/sessions/5eb90a65-846f-4f24-947f-1c0e7ea5090e

Co-authored-by: hotlong <50353452+hotlong@users.noreply.github.com>

Author: Copilot

packages/plugins/plugin-mcp-server/package.json

@@ -0,0 +1,30 @@
+{
+  "name": "@objectstack/plugin-mcp-server",
+  "version": "4.0.2",
+  "license": "Apache-2.0",
+  "description": "MCP Runtime Server Plugin for ObjectStack — exposes AI tools, data resources, and agent prompts via the Model Context Protocol",
+  "type": "module",
+  "main": "dist/index.js",
+  "types": "dist/index.d.ts",
+  "exports": {
+    ".": {
+      "types": "./dist/index.d.ts",
+      "import": "./dist/index.js",
+      "require": "./dist/index.cjs"
+    }
+  },
+  "scripts": {
+    "build": "tsup --config ../../../tsup.config.ts",
+    "test": "vitest run"
+  },
+  "dependencies": {
+    "@modelcontextprotocol/sdk": "^1.29.0",
+    "@objectstack/core": "workspace:*",
+    "@objectstack/spec": "workspace:*"
+  },
+  "devDependencies": {
+    "@types/node": "^25.5.2",
+    "typescript": "^6.0.2",
+    "vitest": "^4.1.2"
+  }
+}

packages/plugins/plugin-mcp-server/src/index.ts

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+// Copyright (c) 2025 ObjectStack. Licensed under the Apache-2.0 license.
+
+/**
+ * @objectstack/plugin-mcp-server
+ *
+ * MCP Runtime Server Plugin for ObjectStack.
+ * Exposes all registered AI tools, data resources, and agent prompts
+ * via the Model Context Protocol (MCP) for use by external AI clients
+ * (Claude Desktop, Cursor, VS Code Copilot, etc.).
+ */
+
+export { MCPServerPlugin } from './plugin.js';
+export type { MCPServerPluginOptions } from './plugin.js';
+export { MCPServerRuntime } from './mcp-server-runtime.js';
+export type { MCPServerRuntimeConfig } from './mcp-server-runtime.js';