ci: trigger Windows autotest dispatch on release publish

[stephamie7]

Summary

• change the flocks autotest dispatch workflow from main push to GitHub release published
• keep workflow_dispatch for manual debugging
• resolve release tag and URL from the published release event before falling back to inputs or pyproject.toml
• pass the first .exe release asset name in the repository_dispatch payload when present

Validation

• git diff --check -- .github/workflows/dispatch-autotest-windows-upgrade.yml
• staged only .github/workflows/dispatch-autotest-windows-upgrade.yml; existing local uv.lock changes were left unstaged

Compatibility

• repository_dispatch event_type is intentionally kept as flocks_main_updated because flocks_autotest/main currently listens for that event type.