fix(infra): drop bad postgres securityContext + un-own shared namespace

Address Codex review on PR #17:

[P1] Postgres official image's entrypoint requires root to chown a
fresh PVC, then drops to the postgres user via gosu. Forcing
runAsNonRoot+runAsUser=999 blocks the chown and initdb fails on a
fresh volume. Drop the securityContext; matches the existing
vaultwarden-postgresql pattern.

[P2] The forte-drop namespace was declared as a managed resource
in the postgres Application. Since minio lives in the same
namespace from a separate Application, an Argo prune of the pg
app would delete the namespace and cascade-delete minio. Remove
the Namespace resource; rely on syncOptions: CreateNamespace=true
on both apps (already set).

infra/overlays/upc-dev/forte-drop-postgresql/resources/postgresql.yaml

@@ -43,13 +43,10 @@ spec:
       containers:
       - name: postgresql
         image: postgres:16-alpine
-        securityContext:
+        # NOTE: no securityContext. The official postgres image's entrypoint must
-          runAsNonRoot: true
+        # start as root to chown a fresh /var/lib/postgresql/data, then drops to
-          runAsUser: 999
+        # the postgres user (uid 70 in alpine) via gosu. Forcing runAsNonRoot here
-          runAsGroup: 999
+        # breaks initdb on a fresh PVC. Matches the vaultwarden-postgresql pattern.
-          allowPrivilegeEscalation: false
-          capabilities:
-            drop: [ALL]
         ports:
         - name: tcp-postgresql
           containerPort: 5432