fix(helm): retain GitLab merge-request links in card facts

[geojitsu]

Intent

Captain wants a direct link to the PR/MR within the Helm sync card body, in the Facts section, so it's easy to jump to it from the card once a PR is opened.

What Changed

• Recognize canonical GitHub pull-request and GitLab merge-request URLs when parsing Helm backlog rows, then retain them as PR facts in card bodies.
• Document the supported URL shapes and add the Helm sync bug record to the documentation audience index.
• Add coverage for valid GitHub and GitLab links and reject malformed or unsupported merge-request paths.

Risk Assessment

✅ Low: The narrowly scoped parser change preserves canonical GitLab MR links alongside existing GitHub PR links, with behavioral coverage for accepted and rejected URL shapes.

Testing

Completed 1 recorded test check.

• Outcome: ⚠️ 1 error across 1 run (19m57s)

Pipeline

Updates from git push no-mistakes

✅ **intent** - passed

✅ No issues found.

✅ **Rebase** - passed

✅ No issues found.

🔧 **Review** - 2 issues found → auto-fixed (2) ✅

• ⚠️ bin/fm-helm-lib.sh:189 - The new MR alternatives accept /merge_requests/0 and numeric prefixes such as /merge_requests/12x; those are rendered as a PR: Facts link despite not being valid MR URLs. The shared PR parser requires a positive, complete IID. Tighten these new patterns to the same number boundary.
• ⚠️ bin/fm-helm-lib.sh:189 - Simplification: /merge_requests/<n> is a new bare-GitLab alias, but the existing canonical PR/MR parser accepts only /-/merge_requests/<n> and no intent requirement calls for the alias. Remove this extra acceptance path and its test unless supporting manually supplied noncanonical GitLab links is intended.

🔧 Fix: Tighten Helm PR URL recognition
1 warning still open:

• ⚠️ docs/bugs/2026-09-14-helm-sync-multi-host-pr-link.md:16 - The new bug note says the allowlist accepts bare GitLab /merge_requests/<number> URLs, but the parser accepts only /-/merge_requests/<number> and the amended integration test asserts that bare URLs are omitted. Update the Fix section to name only the two supported canonical shapes.

🔧 Fix: Correct Helm PR-link documentation
✅ Re-checked - no issues remain.

⚠️ **Test** - 1 error

• 🚨 tests failed with exit code 1
• bin/fm-test-run.sh --changed --exclude-family real-herdr-gated

✅ **Document** - passed

✅ No issues found.

✅ **Lint** - passed

✅ No issues found.

✅ **Push** - passed

✅ No issues found.