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

tsconfig.json

@@ -65,6 +65,7 @@
     { "path": "./packages/todo/tool-todo" },
     { "path": "./packages/hooks/hook-protocol" },
     { "path": "./packages/hooks/hooks-claude" },
-    { "path": "./packages/hooks/hooks-codex" }
+    { "path": "./packages/hooks/hooks-codex" },
+    { "path": "./packages/mcp/mcp-client" }
   ]
 }