fix(anomaly-triage): parse documented bold metadata fields

[ArchonVII]

Problem

The anomaly triage workflow documents metadata as - **Field:** value, but its parser only accepts - **Field**: value. A live caller proof on ArchonVII/sales#39 therefore treated Related to PR: yes as unknown, defaulted severity, and routed the proof entry to a new issue.

Acceptance Criteria

• Parse the documented **Field:** value form for Severity, File, Related to PR, and Downstream repo.
• Preserve compatibility with the legacy **Field**: value form.
• Add regression coverage for both forms and routing-relevant parsed values.
• Verify the reusable workflow remains actionlint-valid.
• Refresh downstream snapshots/pins if the reusable workflow body changes.

Evidence

Discovered during the live verification of #106 in ArchonVII/sales#39 (successful run 29068044608). The proof anomaly used - **Related to PR:** yes but was filed as ArchonVII/sales#41 instead of a related PR comment.