Add MCP smoke test client

docs/mcp.md

@@ -19,7 +19,7 @@ cd /path/to/m2pack-secure
 npm install
 cmake -S . -B build
 cmake --build build -j
-node mcp_server.mjs
+npm run mcp
 ```
 
 ## Environment
@@ -78,6 +78,21 @@ Inputs:
 
 No input. Returns the active `m2pack` binary path.
 
+## Smoke test
+
+Run a local roundtrip test with the bundled Node MCP client:
+
+```bash
+npm run mcp:smoke
+```
+
+That test:
+
+- spawns `mcp_server.mjs`
+- connects over stdio
+- lists tools
+- calls `pack_binary_info`
+
 ## Claude Desktop style config example
 
 ```json