- Replace single-branch push trigger with test + main + workflow_dispatch
- Add environment determination (test → PATCH bump, main/prod → MINOR bump)
- Add semver calculation with conditional patch/minor logic
- Add env validation (fails early on invalid env)
- Remove pa- prefix from git tags (use plain semver)
- Test builds fresh image; main/prod promotes test image to prod
- Match final architecture spec from Archie