feat: add MCP client plugin (dsh-mcp-client)

Connects to an external MCP server and registers its tools on
ctx.tools. Supports stdio (child process) and Streamable HTTP
transports. Credential-shaped env vars are scrubbed before forwarding
to child processes.

- Plugin lifecycle: connect, sync tools, re-sync on ToolListChanged,
  dispose unregisters and closes
- Full JSDoc on all exports (@param/@returns on functions)
- 100% per-file coverage (apply lifecycle, args coercion, env scrubbing)
- Config catalog regenerated

packages/mcp/mcp-client/package.json

@@ -33,9 +33,6 @@
   "devDependencies": {
     "@deepseek-ai/dsh-tools": "workspace:^",
     "@deepseek-ai/dsh-llm": "workspace:^",
-    "@modelcontextprotocol/server-everything": "^2026.7.4",
-    "@modelcontextprotocol/server-filesystem": "^2026.7.4",
-    "cordis": "^4.0.0-rc.6",
-    "zod": "^4.4.3"
+    "cordis": "^4.0.0-rc.6"
   }
 }