Automate miner release versioning

[n13]

Summary

Replaces the manual version-entry miner release with the same automated flow as quantus-cli / chain / quantus-miner:

• create_miner_release_proposal.yml (new): dispatch with patch/minor/major/custom. Computes the next version from the latest miner-v* tag, bumps miner-app/pubspec.yaml, and opens a PR labeled miner-release-proposal (labels auto-created on first run).
• publish_miner_release.yml (new): when that PR merges — verifies pubspec matches, tags the merge commit miner-vX.Y.Z, builds all platforms at the tag, and publishes the GitHub release (gh release create, with --notes-start-tag pinned to the previous miner tag so generated notes don't diff against wallet-v* tags).
• create_miner_build.yml: now build-only and reusable (workflow_call with a ref input); manual dispatch still available for test builds. The old in-workflow release job (deprecated actions/create-release@v1) is removed.

Notes

• The proposal uses the PAT_TOKEN secret for gh pr create so CI triggers on the release PR (same as ADMIN_PAT in the other repos). If it has expired, the proposal job fails at PR creation and the secret needs rotating.
• main is already at pubspec 0.5.0 (manual bump) while the latest tag is miner-v0.4.5, so the proposal commit allows an empty diff; for the first run choose minor to release miner-v0.5.0.

Test plan

• actionlint clean (one pre-existing info-level note in the untouched Linux tar step)
• Version bump math, pubspec sed, and previous-tag lookup verified locally against the real tag list
• After merge: run the proposal workflow with minor, merge the bump PR, confirm tag + 3-platform release

[dewabisma]

Have you tested the CI workflows? It can be tricky to make CI works without actually run and see it works.

[n13]

Yes thats why i did not merge yet ;)