refactor: rename all custom K8s components to hightower

Namespace, Temporal, router, PVCs, labels, and GHCR API image all
renamed from shannon-* to hightower-*. Upstream references preserved:
worker image (ghcr.io/farhoodliquor/shannon), .shannon/ dirs,
@shannon/worker package imports.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -101,5 +101,5 @@ jobs:
           file: apps/api/Dockerfile
           push: true
           tags: |
-            ghcr.io/farhoodliquor/shannon-api:latest
-            ghcr.io/farhoodliquor/shannon-api:sha-${{ github.sha }}
+            ghcr.io/farhoodliquor/hightower-api:latest
+            ghcr.io/farhoodliquor/hightower-api:sha-${{ github.sha }}