Add gonic playlist ownership fix references

[cookesan]

Adds gonic playlist ownership fix references to GHSA-hmgp-w9jm-vp95.

Audit refresh, July 8, 2026:

• Confirmed the live PR is open, ready for review, merge-clean, and the visible advisory check is green.
• Rechecked the merge-base diff: exactly one advisory JSON file changes (advisories/github-reviewed/2026/06/GHSA-hmgp-w9jm-vp95/GHSA-hmgp-w9jm-vp95.json), JSON parses, git diff --check passes, and the exact-head worktree is clean.
• Revalidated the added public references in the diff; all resolve through their source site or registry.

[cookesan]

Revalidated July 8, 2026: this remains scoped to gonic v0.21.0 fixed-release evidence for GHSA-hmgp-w9jm-vp95 and expanding the existing short fix commit to the full commit URL. The Go module page, upstream tag, and full fix commit resolve; affected range, severity, and advisory metadata fields remain unchanged. Local checks passed with a single advisory JSON file changed, JSON parsing, git diff --check HEAD^..HEAD, and a clean worktree.