Enable Grafana panel embedding and public dashboards

- allow_embedding: true - allows iframe embedding
- cookie_samesite: lax - fixes session cookies in iframes
- public_dashboards: enabled - per-dashboard public sharing via UI

Public dashboard settings persist in SQLite DB on PVC.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

argocd/manifests/grafana/values.yaml

@@ -25,6 +25,15 @@ persistence:
 grafana.ini:
   server:
     root_url: https://grafana.tail8d86e.ts.net
+  security:
+    # Allow embedding panels in iframes (for Homepage dashboard)
+    allow_embedding: true
+    # Required for iframe session cookies
+    cookie_samesite: lax
+  # Public dashboards - selectively share specific dashboards without auth
+  # Enable per-dashboard via Share > Public Dashboard in Grafana UI
+  public_dashboards:
+    enabled: true
   analytics:
     check_for_updates: false
     reporting_enabled: false