Mirrors the Elixir wiring:
- ImageRepository + ImagePolicy scan git.mcintire.me/graham/prop-grid-rs
for main-<ts>-<sha> tags and pick the highest timestamp.
- ImageUpdateAutomation already covers ./k8s via the Setters strategy,
so the new setter marker on deployment-grid-rs.yaml means flux will
rewrite it on every CI push and commit the update back to main.
