Implement fixes from test results

- Update Docker install to use curl method
- Rename ADMIN_PASSWORD to AUTHELIA_ADMIN_PASSWORD
- Fix Authelia password hash generation (remove grep, no quotes)
- Revert compose labels to single quotes
- Ensure users_database.yml has unquoted password placeholder

.env.example

@@ -60,6 +60,7 @@ ACME_EMAIL=${DEFAULT_EMAIL}
 ADMIN_EMAIL=${DEFAULT_EMAIL}  # Used for admin user account
 AUTHELIA_ADMIN_USER=${DEFAULT_USER}
 AUTHELIA_ADMIN_EMAIL=${DEFAULT_EMAIL}
+AUTHELIA_ADMIN_PASSWORD=${DEFAULT_PASSWORD}
 AUTHELIA_ADMIN_PASSWORD_HASH=generate-with-openssl-rand-hex-64
 
 # SMTP for Authelia Notifications