part5c of work towards rel v25.9.1 (crossbario#1698)

* Clean up legacy build configuration and archived workflows

Removed obsolete files after completing migration to modern build system
(justfile + uv + pyproject.toml + new GitHub Actions workflows).

Deleted legacy build configuration files:
- Makefile (archived as Makefile.orig for reference)
- tox.ini (replaced by uv + justfile recipes)
- setup.cfg (flake8 config, replaced by ruff in pyproject.toml)

Deleted old development scripts:
- inject-build-id.py (only used in archived workflows)
- docker-bake.hcl (not referenced in active workflows)
- copy_project_templates.py (dev utility, not part of CI/CD)

Deleted legacy backup files:
- setup.py.old

Removed archived workflow directory:
- .github/workflows/.old/ (5 old workflow files)
  All archived workflows have been replaced with modern equivalents

All removed files remain available in git history if needed.

Kept essential files:
- setup.py (CRITICAL: CFFI module building for NVX extensions)
- mypy.ini (mypy type checker configuration)
- pytest.ini (pytest configuration)
- Makefile.orig (archive)

* Support workflow_dispatch trigger in release workflow

The release workflow was only designed for workflow_run triggers,
causing errors when manually triggered via workflow_dispatch.

Changes:
1. Handle both trigger types when getting commit SHA:
   - workflow_run: use context.payload.workflow_run.head_sha
   - workflow_dispatch: use context.sha

2. Updated job conditions to accept both triggers:
   - workflow_dispatch (manual trigger)
   - workflow_run (automatic trigger after other workflows)

This allows manual testing of the release workflow, which is essential
for fork PRs where workflow_run doesn't trigger due to GitHub's
security restrictions.

Now you can manually trigger the release workflow to test it!

Author: oberstet