Adds a build-dev job to ci.yml that fires after tests pass on direct
pushes to dev (not PRs). Pushes two tags to the registry:
:dev — mutable, always the latest integrated dev state
:dev-<sha> — immutable, for tracing exactly which commit is running
Staging servers can pull :dev to test before a release PR is opened.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>