ci(release): standardize fleet publish and validation flow

[JSONbored]

Summary

• remove the unused automation flag and align release-triggered publishing with the fleet baseline

What changed

• remove ENABLE_AIO_AUTOMATION gating from workflow behavior and validation helpers
• make publish jobs explicitly require push to main
• update release docs to the current prepare-then-publish flow

Why

• the fleet does not use ENABLE_AIO_AUTOMATION
• release/package behavior should be explicit and consistent across repos

Validation

• trunk check --show-existing --all
• python3 scripts/validate-template.py
• pytest tests/unit tests/template
• pytest tests/integration -m integration
• pytest tests/unit tests/template --junit-xml=reports/pytest-unit.xml -o junit_family=xunit1
• pytest tests/integration -m integration --junit-xml=reports/pytest-integration.xml -o junit_family=xunit1
• /tmp/trunk-analytics-cli/trunk-analytics-cli validate --junit-paths "reports/pytest-unit.xml,reports/pytest-integration.xml"
• git diff --check