ci: re-enable GitHub Actions after pipeline refactor

[sighook]

GitHub Actions are currently disabled for this repository pending the completion of the transition to the new event-aware delivery pipeline.

Context

• Current State: Disabled to prevent reliance on deprecated or unmanaged workflow templates.
• Tracking Issue: automation/workflows: replace notification templates with an event-aware delivery pipeline #1

Action Required

Before re-enabling Actions in this repository, ensure that:

1. The new reusable workflows in the automation repository have been stabilized.
2. The event-aware delivery pipeline is verified to function within this environment.
3. Repository secrets and environment-specific configurations are mapped to the new delivery model.

Note: Do not re-enable until the upstream changes in the automation repo have been merged and tagged.