Deploy ECS automatically after application merges

[ali509]

Summary

• trigger the ECS deployment workflow for application changes pushed to main
• default automatic deployments to the protected dev environment
• retain manual workflow dispatch and image-only publishing
• keep the EC2 CodeDeploy workflow manual
• document the automatic ECS release behavior

Validation

• workflow YAML parsed successfully
• whitespace validation passed

Deployment behavior

Merging this PR triggers the first automatic ECS deployment because the workflow file itself is included in the push path filter.