PROJQUAY-12344: docs: align Contributing format with repo convention (#1305)

[fullsend-ai-coder]

Update the Contributing section of AGENTS.md to match the actual commit and PR title convention used in this repository. The documented format had the Jira reference at the end (: (PROJQUAY-####)), but every recent commit and PR uses the Jira-first format (PROJQUAY-####: : ), which is what the Prow/Jira integration validates.

Changes:

• Document PR title format alongside commit message format
• Change format to Jira-first: PROJQUAY-####: :
• Add NO-ISSUE: prefix for non-Jira changes
• Clarify that the subsystem prefix is required in both PR titles
  and commit messages

---

Closes #1305

Post-script verification

• Branch is not main/master (agent/1305-fix-contributing-format)
• Secret scan passed (gitleaks — 691a3b42526b1b2f98a1eac0a033a28c3e445a7c..HEAD)
• Pre-commit hooks passed (authoritative run on runner)
• Tests ran inside sandbox

[openshift-ci-robot]

@fullsend-ai-coder[bot]: This pull request references [Jira Issue PROJQUAY-12344](https://redhat.atlassian.net/browse/PROJQUAY-12344), which is invalid:

• expected the bug to target the "quay-v3.18.0" version, but no target version was set
• expected the bug to be in one of the following states: NEW, ASSIGNED, POST, but it is MODIFIED instead

Comment /jira refresh to re-evaluate validity if changes to the Jira bug are made, or edit the title of this pull request to link to a different bug.

Details

In response to this:

Update the Contributing section of AGENTS.md to match the actual commit and PR title convention used in this repository. The documented format had the Jira reference at the end (: (PROJQUAY-####)), but every recent commit and PR uses the Jira-first format (PROJQUAY-####: : ), which is what the Prow/Jira integration validates.

Changes:

• Document PR title format alongside commit message format
• Change format to Jira-first: PROJQUAY-####: :
• Add NO-ISSUE: prefix for non-Jira changes
• Clarify that the subsystem prefix is required in both PR titles
  and commit messages

---

Closes #1305

Post-script verification

• Branch is not main/master (agent/1305-fix-contributing-format)
• Secret scan passed (gitleaks — 691a3b42526b1b2f98a1eac0a033a28c3e445a7c..HEAD)
• Pre-commit hooks passed (authoritative run on runner)
• Tests ran inside sandbox

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the openshift-eng/jira-lifecycle-plugin repository.

[openshift-ci]

Hi @fullsend-ai-coder[bot]. Thanks for your PR.

I'm waiting for a quay member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work.

Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

I understand the commands that are listed here.

Details

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.