fix(deploy): auto-migrate on boot + seed admin credentials from env

- docker-compose.admin.yml: RUN_MIGRATIONS was hardcoded false → now
  uses ${RUN_MIGRATIONS:-true} so migrations run automatically on deploy
- Both compose files: expose Seed__SystemAdminPhone/Username/Password
  env vars so the seeder sets admin credentials without manual SQL
- .env.example: document SEED_ADMIN_* variables

On next deploy: migrations run, Username='admin' is patched on the
existing admin, and password is hashed from SEED_ADMIN_PASSWORD.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.env.example

@@ -68,6 +68,14 @@ REDIS_PORT=6381
 # ── Migrations ────────────────────────────────────────────────────────────────
 RUN_MIGRATIONS=true
 
+# ── System admin seed (admin panel login) ─────────────────────────────────────
+# On every boot the seeder ensures this admin exists with these credentials.
+# Username defaults to "admin" if not set. Password is required to enable
+# password login — leave blank to force OTP-only login.
+SEED_ADMIN_PHONE=09190345606
+SEED_ADMIN_USERNAME=admin
+SEED_ADMIN_PASSWORD=change-me-strong-admin-password
+
 # ── Payment: ZarinPal ─────────────────────────────────────────────────────────
 # Get your merchant ID from: https://panel.zarinpal.com → API → MerchantID
 ZARINPAL_MERCHANT_ID=