fix(container/image_versions): reject entries that are not image references

The parser retained any key ending in _IMAGE, so a harmless-looking
variable like NOT_AN_IMAGE="something" would be treated as a pinned
container image. Add a value-shape check: the value must contain both
a registry separator (/) and a tag separator (:) to qualify.

core/archipelago/src/container/image_versions.rs

@@ -107,8 +107,11 @@ fn parse_image_versions(content: &str) -> HashMap<String, String> {
         }
     }
 
-    // Keep only *_IMAGE entries
-    vars.retain(|k, _| k.ends_with("_IMAGE"));
+    // Keep only *_IMAGE entries whose value looks like a container image
+    // reference (contains a `:` tag separator and at least one `/` path
+    // component). Rejects placeholder values like "something" so a
+    // hand-edit typo in image-versions.sh never gets treated as an image.
+    vars.retain(|k, v| k.ends_with("_IMAGE") && v.contains(':') && v.contains('/'));
     vars
 }