Fix tagbot deployment of automatic github releases.

[bparbhu]

Summary

The v4.12.4 release was successfully registered in the General registry via JuliaHub,
but TagBot failed to create the corresponding Git tag and GitHub Release.

TagBot error:

git@github.com: Permission denied (publickey)

This indicates that TagBot does not currently have permission to push tags
(using the DOCUMENTER_KEY SSH configuration).

Impact

• The package is installable via Pkg.add("StanBase")
• However, the GitHub release and tag were not automatically created
• Several historical versions were also flagged by TagBot as missing releases

Immediate Action Taken

We manually created the tag and GitHub release for v4.12.4.

Proposed Fix

Switch TagBot to use a Personal Access Token (PAT) instead of SSH,
or correctly configure the DOCUMENTER_KEY deploy key with write access.

Recommended approach:

• Add a fine-grained PAT with contents: write permissions

• Store as TAGBOT_TOKEN

• Update .github/workflows/TagBot.yml to use:

  with:
  token: ${{ secrets.TAGBOT_TOKEN }}

This avoids SSH deploy key fragility and simplifies maintenance.

Next Steps

• Update TagBot workflow
• Verify automatic tag + release on next version bump
• Perform a fast-follow release to confirm automation works end-to-end

This will restore fully automated Julia package releases for StanBase.