debug: clean up Setters investigation debris

Remove the throwaway setter-test.yaml and revert update.path to
./apps/hello-app. Root cause of ImageUpdateAutomation never committing a
tag update remains unresolved after exhausting marker syntax, path
scoping, field structure, namespace placement, RBAC, and version
compatibility as candidates - all checked out fine individually. Moving
on to docs/04-tofu.md; may retest after Flux gets a fresh bootstrap
against the new cluster there.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Y4YNpuC2bgT224suQLLJ7B

apps/hello-app/image-automation.yaml

@@ -53,5 +53,5 @@ spec:
     push:
       branch: main
   update:
-    path: ./
+    path: ./apps/hello-app
     strategy: Setters