Release `v*` tags no longer publish semver Docker images (regression since #1126)

Summary

Formal releases are no longer producing versioned Docker images. The README states that "formal releases use version tags (e.g., v2.26.0)," but no semver-tagged image has been published for any release since v2.25.8. Releases v2.26.0 → v2.30.0 exist as Git tags with no corresponding image on either registry.

Evidence

GHCR (ghcr.io/elie222/inbox-zero)

• Highest semver image tag present: v2.25.8 (HTTP 200)
• v2.30.0 → HTTP 404 (does not exist)
• latest is current (commit c7a640d, built 2026-07-19)

Docker Hub (docker.io/elie222/inbox-zero)

• v2.30.0, v2.29.3, v2.26.0 → all HTTP 404
• Only SHA tags + latest have been pushed for the last ~7 months
• latest → HTTP 200 (current)

Git releases (for contrast) — all exist: v2.26.0, v2.27.0, v2.29.0–v2.29.3, v2.30.0.

Likely cause

This lines up with #1126 ("Use sha versioning," merged Dec 20, 2025), which changed .github/workflows/build_and_publish_docker.yml to trigger on v* tags and derive semver image tags via docker/metadata-action@v5. The last successful semver image (v2.25.8) is right around that cutover, so it appears the v*-tag-triggered build either isn't firing or isn't pushing semver tags for releases cut after the merge. Push-to-main builds (SHA + latest) are working fine.

Worth checking:

• Are releases created via a Git tag push (which fires on: push: tags: ['v*']), or via the GitHub Releases UI / a bot that may not trigger push?
• Does the Depot push step receive the semver tags from metadata-action on tag-triggered runs?
• Any recent tag-triggered workflow runs in the Actions history, and did they succeed?

Impact

Users can't pin to a released version — docker pull ...:v2.30.0 fails on both registries. The only reproducible option today is pinning to a commit SHA (e.g. ghcr.io/elie222/inbox-zero:c7a640d), which isn't discoverable from the release notes.

Suggested fix

Restore semver image publishing on release, and/or update the README to reflect that only latest + SHA tags are currently published.