Add Trivy CVE scan, container registry docs, and update diagrams

- Add Trivy vulnerability scan step to CI (HIGH/CRITICAL, warn-only)
- Add Container Registry section to README with pull examples
- Update architecture doc and HLD with crane + Trivy details

Co-authored-by: Cursor <cursoragent@cursor.com>

docs/architecture-hld.md

@@ -29,7 +29,7 @@ flowchart TB
                     Blue[Blue — new release<br/>smoke tests]
                 end
                 subgraph Workloads
-                    API[Backend — Python / Flask<br/>HPA · 2–3 replicas]
+                    API[Backend — Python / Flask<br/>HPA · 2-3 replicas]
                     SPA[Frontend — React SPA<br/>Nginx]
                 end
                 Redis[Redis — Memorystore<br/>Session / Cache]
@@ -94,8 +94,9 @@ flowchart LR
 flowchart LR
     Dev[Developer] -->|push| Repo[Git Repo]
     Repo -->|webhook| CI[CI Pipeline<br/>lint · test · build]
-    CI -->|docker build + push| Registry[Container Registry<br/>Artifact Registry / Gitea OCI]
-    CI -->|scan image| Trivy[Trivy<br/>CVE scan]
+    CI -->|crane copy / docker push| Registry[Container Registry<br/>Artifact Registry / Gitea OCI]
+    Registry -->|scan image| Trivy[Trivy<br/>HIGH + CRITICAL CVEs]
+    Trivy -->|pass| CI2[Publish Release]
     CI -->|update manifests| GitOps[GitOps Repo]
     GitOps -->|sync| Argo[ArgoCD]
     Argo -->|blue-green deploy| GKE[GKE Cluster]