feat(flux): add image-automation for prop-grid-rs

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.

k8s/deployment-grid-rs.yaml

@@ -48,7 +48,7 @@ spec:
           # Image built by a new CI pipeline from rust/prop_grid_rs/.
           # Multi-arch (amd64 + arm64) — reuses the repo's existing
           # buildx wiring.
-          image: git.mcintire.me/graham/prop-grid-rs:main
+          image: git.mcintire.me/graham/prop-grid-rs:main # {"$imagepolicy": "flux-system:prop-grid-rs"}
           imagePullPolicy: IfNotPresent
           env:
             # Elixir secrets bundle carries DATABASE_URL already. Rust

k8s/flux.yaml

@@ -54,6 +54,33 @@ spec:
     extract: $ts
 ---
 apiVersion: image.toolkit.fluxcd.io/v1
+kind: ImageRepository
+metadata:
+  name: prop-grid-rs
+  namespace: flux-system
+spec:
+  image: git.mcintire.me/graham/prop-grid-rs
+  interval: 1m
+  provider: generic
+  secretRef:
+    name: forgejo-registry
+---
+apiVersion: image.toolkit.fluxcd.io/v1
+kind: ImagePolicy
+metadata:
+  name: prop-grid-rs
+  namespace: flux-system
+spec:
+  imageRepositoryRef:
+    name: prop-grid-rs
+  policy:
+    numerical:
+      order: asc
+  filterTags:
+    pattern: ^main-(?P<ts>[0-9]+)-[a-f0-9]+$
+    extract: $ts
+---
+apiVersion: image.toolkit.fluxcd.io/v1
 kind: ImageUpdateAutomation
 metadata:
   name: prop