feat: add Docker first-start admin bootstrap

.env.example

@@ -8,10 +8,10 @@ COOKIE_SECURE=false
 SESSION_SECRET=bzod-default-session-secret-change-me-in-production-please-do-it
 
 # Bootstrap Admin Credentials
-# Default username: admin
-# Default password: admin
 ADMIN_USERNAME=admin
-ADMIN_PASSWORD_SHA256=8c6976e5b5410415bde908bd4dee15dfb167a9c873fc4bb8a81f6f2ab448a918
+# REQUIRED for a fresh deployment.
+# Use a strong unique password.
+ADMIN_PASSWORD=
 
 # Cron & Cleaner Intervals (in minutes)
 LINK_CHECK_INTERVAL_MINS=60