Clarify end-of-run warnings to mention lowering n_parallels and label API connection errors

[hemanth-asirvatham]

Motivation

• Make end-of-run, user-facing guidance explicit about how to reduce concurrency by lowering n_parallels so operators have a clear action to follow.
• Make connection-error messaging unambiguous by referring to them as API connection errors and call out network instability or bandwidth limits as likely causes.

Description

• Update wording in src/gabriel/utils/openai_utils.py end-of-run warnings to recommend "reducing concurrency via lower n_parallels." for rate-limit guidance.
• Replace the generic connection-error warning with: an API connection errors label and the sentence ...indicating network instability or bandwidth limitations; consider reducing concurrency via lower n_parallels.

Testing

• No automated tests were run for this change.

---

Codex Task

[github-actions]

Thank you for your submission, we really appreciate it. Like many open-source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution. You can sign the CLA by just posting a Pull Request Comment same as the below format.

---

I have read the CLA Document and I hereby sign the CLA

---

_{You can retrigger this bot by commenting recheck in this Pull Request. Posted by the CLA Assistant Lite bot.}