Prerequisites

• I searched existing issues

Feature Description

When a docs/vX.Y.Z tag is pushed, the publish workflow should automatically:

1. Generate fern/versions/vX.Y.Z.yml from the tag's docs/index.yml
2. Add a version entry to fern/docs.yml
3. Commit both back to main

Currently version entries must be created manually, which is error-prone and easy to forget after a release.

Additionally, the frozen version checkout should be hardened:

• Guard against missing glob matches
• Warn instead of failing hard on missing tags
• Fix non-self-closing <img> tags in older tagged content (MDX safety)
• Use yq instead of sed for YAML manipulation (version stamping)

Pattern proven in NVIDIA/topograph PRs #325, #327, #329, #330.