fix(engineering): correct GitHub MCP server URL (#172)

api.github.com/mcp returns 404 — the route does not exist.
Correct endpoint is api.githubcopilot.com/mcp/ (verified from
claude-plugins-official/external_plugins/github/.mcp.json).

Fixes #168

Author: tejas-dharani

engineering/.mcp.json

@@ -26,7 +26,7 @@
     },
     "github": {
       "type": "http",
-      "url": "https://api.github.com/mcp"
+      "url": "https://api.githubcopilot.com/mcp/"
     },
     "pagerduty": {
       "type": "http",