chore: DB defaults for managed platform, reduce required env vars

- db.js: DB_HOST default postgresqlk8s-master, DB_NAME default ipwhitelist, DB_USER default super
- server.js: fail-fast for DB_PASS in production (instead of IAM_API_URL)
- After this change: only DB_PASS is required for mock mode

server.js

@@ -70,8 +70,8 @@ async function start() {
       console.error('FATAL: SESSION_SECRET не задан или равен дефолту в production!');
       process.exit(1);
     }
-    if (!process.env.IAM_API_URL) {
-      console.error('FATAL: IAM_API_URL не задан в production!');
+    if (!process.env.DB_PASS) {
+      console.error('FATAL: DB_PASS не задан в production!');
       process.exit(1);
     }
   }