Fix dev-deploy.yml: deploy triggering commit instead of tip of dev branch

[Copilot]

dev-deploy.yml was hardcoding ref: dev, causing it to always build and push whatever was at the current tip of dev — not the specific commit that passed CI. This creates a race condition where newer, untested commits get deployed.

Change

• dev-deploy.yml: Replace ref: dev with ref: ${{ github.event.workflow_run.head_sha }} — the same pattern prod-deploy.yml already uses correctly.

# before
- uses: actions/checkout@v6.0.3
  with:
    ref: dev

# after
- uses: actions/checkout@v6.0.3
  with:
    ref: ${{ github.event.workflow_run.head_sha }}

github.event.workflow_run.head_sha is the exact commit SHA that triggered the upstream CI workflow, so the deployed image will always correspond to the code that was actually tested.