Add nebula-mesh fixed release reference

[cookesan]

Adds nebula-mesh fixed release reference to GHSA-598g-h2vc-h5vg.

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-598g-h2vc-h5vg/GHSA-598g-h2vc-h5vg.json), JSON parses, git diff --check passes, and the exact-head worktree is clean.
• Revalidated the added public references and package-version evidence in the diff; all resolve through their source site or registry.

[cookesan]

Rechecked this reference-only PR while keeping the open Advisory Database queue current.

• The patch only adds the nebula-mesh v0.3.4 release reference; it does not change affected ranges, package metadata, or severity.
• The release tag resolves as v0.3.4.
• The fixed version in the advisory remains 0.3.4.

No other advisory fields are changed.