fix: send a User-Agent on every outbound request

[CodeWithJuber]

Found by calling github.get_repo through a live MCP session.

reqwest sends no User-Agent by default, and GitHub rejects requests without one:

403 Request forbidden by administrative rules. Please make sure your request
has a User-Agent header

That is all 25 github operations failing before authentication is even considered. The failure mode is the expensive part: it surfaces as a generic network error, so it reads as a credential problem, and no amount of fixing the token makes it go away. Several WAF-fronted provider APIs reject UA-less traffic the same way.

Both Client::builder() call sites (new and with_timeout) were also duplicating timeout and redirect config. Collapsed into one build_client(timeout_secs) so a future transport setting cannot be added to one path and forgotten on the other.

The UA is connector-hub/<CARGO_PKG_VERSION> (+https://github.com/CodeWithJuber/connector-hub) — version comes from the crate, so it tracks releases without a second place to update.

Verification

Same operation, same credentials, before and after:

before:  network error: HTTP error 403: Request forbidden by administrative rules...
after:   network error: HTTP error 401: {"message": "Bad credentials", ...}

401 is the correct answer here — that token is expired. The point is the request now reaches GitHub's auth layer at all.

cargo fmt --check                       ok
cargo clippy --all-targets -D warnings  ok
cargo test --workspace                  26 passed
connector-hub validate                  passed

🤖 Generated with Claude Code

https://claude.ai/code/session_018Xs4hZtZhd9Vi6EJnVnwDf