Include meaningful User-Agent header in requests to the GitHub UI

This adds a custom `User-Agent` header to requests from the
GitHub server to the GitHub API, identifying the application,
the version and key information about the environment.

This aligns with the [recommendations][1] in the GitHub Docs.

As part of this change, I have also moved the current version of
the server into a constant, and fix the initialization of `Server`
to use that version, taking from `package.json`.

[1]: https://docs.github.com/en/rest/using-the-rest-api/getting-started-with-the-rest-api?apiVersion=2022-11-28#user-agent

src/github/package.json

@@ -23,6 +23,7 @@
     "@types/node": "^22",
     "@types/node-fetch": "^2.6.12",
     "node-fetch": "^3.3.2",
+    "universal-user-agent": "^7.0.2",
     "zod": "^3.22.4",
     "zod-to-json-schema": "^3.23.5"
   },
@@ -30,4 +31,4 @@
     "shx": "^0.3.4",
     "typescript": "^5.6.2"
   }
-}
+}