[Bug] volcano-sh-bot incorrectly flags Co-authored-by commits as invalid

[codeEvolveZenith345]

Description

The volcano-sh-bot commit message validator incorrectly flags legitimate commits containing Co-authored-by trailers as having "invalid commit messages", claiming they contain "@" mentions or issue-closing keywords when they do not.

Current Behavior

When accepting code suggestions from GitHub bots (Gemini Code Assist, Copilot, etc.), commits automatically include standard Co-authored-by trailers per [GitHub convention](https://docs.github.com/en/pull-requests/committing-changes-to-your-project/creating-and-editing-commits/creating-a-commit-with-multiple-authors):

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

The bot then flags these as invalid:

Keywords which can automatically close issues and at(@) or hashtag(#) mentions 
are not allowed in commit messages.

The list of commits with invalid commit messages:
047ddf3 Update README.md

Expected Behavior

The bot should ignore Co-authored-by trailers when validating commit messages, as:

1. These are standard Git/GitHub convention for attribution
2. Email addresses in trailers are not @ mentions
3. They don't contain issue-closing keywords
4. They're automatically generated by GitHub's UI

Steps to Reproduce

1. Create a PR to volcano-sh/website
2. Accept a code suggestion from any GitHub bot (Gemini, Copilot, etc.)
3. Observe the do-not-merge/invalid-commit-message label applied
4. Force-push to squash/remove the co-authored commits
5. Observe the label removed (proving the commit message body was valid)

Evidence

From PR #445 #446 :

• Commits 047ddf3 and 9c6fcdd flagged as invalid
• Both contain only "Update README.md" in subject/body
• Only "violation" is the Co-authored-by trailer
• After force-push removing trailers, label automatically removed

Impact

• Blocks legitimate contributions that use GitHub's native collaboration features
• Creates confusion for new contributors
• Wastes reviewer time investigating false positives
• Discourages use of code review bots (Gemini, Copilot, etc.)

Proposed Fix

Update the bot's commit message validation regex to exclude Co-authored-by trailers from:

1. "@" mention detection
2. Issue keyword detection

Example exclusion pattern:

# Ignore lines matching Co-authored-by trailer format
^Co-authored-by: .+ <.+@.+>$

Environment

• Repository: volcano-sh/website
• Bot: volcano-sh-bot
• Trigger: Any commit with Co-authored-by trailer
• PR Example: #[your-pr-number]

Related

• [GitHub Docs: Creating commits with multiple authors](https://docs.github.com/en/pull-requests/committing-changes-to-your-project/creating-and-editing-commits/creating-a-commit-with-multiple-authors)
• Standard Git trailer format: [git-interpret-trailers](https://git-scm.com/docs/git-interpret-trailers)

---

Labels: kind/bug, area/ci, priority/medium

cc @JesseStutler @william-wang @de6p

[codeEvolveZenith345]

/assign

[codeEvolveZenith345]

@JesseStutler @Arhell @amye Please approve if my observation is correct. I will start working on the fix.