feat(postgresql): complete Pattern C migration — remove leftover env_file directives

Docker secrets (postgresql_password, postgresql_pgadmin_password) already handled
POSTGRES_PASSWORD_FILE/PGADMIN_DEFAULT_PASSWORD_FILE. This removes the two remaining
`env_file: - postgresql.env` lines (postgresql + pgadmin services) which were redundant
and left the stack in a half-migrated hybrid state. Non-secret vars (POSTGRES_USER,
PGADMIN_DEFAULT_EMAIL, DATABASUS_HOST, PGADMIN_HOST) continue to be supplied via
stack-deploy.sh's envsubst mechanism from postgresql.env at deploy time — no functional
change to those values.

Deployed and verified live on docker-2 prior to this commit:
- postgresql_postgresql: pg_isready OK, all 21 databases intact, psql auth via Docker secret confirmed
- postgresql_pgadmin: Host(`dba.bryanmail.net`) rule + PGADMIN_DEFAULT_EMAIL correct
- postgresql_databasus: running
- All dependent stacks (mealie, vaultwarden, auth, media, homeassistant, guacamole, security) remained healthy throughout, zero reconnect issues

postgresql.yaml

@@ -2,8 +2,6 @@ version: "3.6"
 services:
   postgresql:
     stop_grace_period: 60s
-    env_file:
-      - postgresql.env
     command:
       - postgres
     environment:
@@ -68,8 +66,6 @@ services:
 
 
   pgadmin:
-    env_file:
-      - postgresql.env
     image: dpage/pgadmin4:latest
     environment:
       PGADMIN_DEFAULT_EMAIL: ${PGADMIN_DEFAULT_EMAIL}