fix(infra): add headroom MCP to minimal config

Headroom handles token/context compression, so keep it in the reduced MCP
server list.

.mcp.json

@@ -90,6 +90,12 @@
       "headers": {
         "Authorization": "Bearer ${GITHUB_PERSONAL_ACCESS_TOKEN}"
       }
+    },
+    "headroom": {
+      "_comment": "Headroom token compression / context compression proxy.",
+      "command": "/home/allaun/.local/share/pipx/venvs/headroom-ai/bin/python",
+      "args": ["-E", "/home/allaun/.local/bin/headroom", "mcp", "serve"],
+      "env": {}
     }
   }
 }