C1: pin shower image tag to v1.0.0-118cbbf-nix (run 536)

Build 536 finished cleanly with the strip-refs FOD + autopatchelf
wrapper. The [branch] tag is fine for ArgoCD branch-revision testing;
a follow-up C0 will rebuild from main and re-pin to the [main] SHA tag
after merge, per docs/how-to/deployment/build-container-image.md.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

argocd/manifests/shower/kustomization.yaml

@@ -14,4 +14,4 @@ resources:
 
 images:
   - name: registry.ops.eblu.me/blumeops/shower
-    newTag: v1.0.0-PLACEHOLDER-nix
+    newTag: v1.0.0-118cbbf-nix