feat(grafana): migrate from SQLite/PVC to PostgreSQL backend

Grafana now stores users, preferences, and state in our existing
PostgreSQL instance (dedicated 'grafana' database). This eliminates
the 2Gi PVC dependency — all persistent state lives in Postgres,
dashboards in ConfigMaps, datasources in Helm values.

Also adds Grafana to Postgres NetworkPolicy ingress allowlist.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

infra/k8s/gitlab/grafana-values.yaml

@@ -21,15 +21,24 @@ resources:
     memory: 256Mi
 
 persistence:
-  enabled: true
-  size: 2Gi
+  enabled: false
 
 adminUser: admin
 adminPassword: Welcome01
 
+envFromSecrets:
+  - name: db-credentials
+
 grafana.ini:
   server:
     root_url: https://grafana.fxhnt.ai
+  database:
+    type: postgres
+    host: postgres:5432
+    name: grafana
+    user: foxhunt
+    password: $__env{password}
+    ssl_mode: disable
 
 datasources:
   datasources.yaml:

infra/k8s/network-policies/infrastructure.yaml

@@ -1,4 +1,4 @@
-# Postgres: accepts connections from foxhunt app pods + GitLab (Helm release)
+# Postgres: accepts connections from foxhunt app pods, GitLab, and Grafana
 apiVersion: networking.k8s.io/v1
 kind: NetworkPolicy
 metadata:
@@ -20,6 +20,9 @@ spec:
         - podSelector:
             matchLabels:
               release: gitlab
+        - podSelector:
+            matchLabels:
+              app.kubernetes.io/name: grafana
       ports:
         - protocol: TCP
           port: 5432