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

config-templates/authelia/users_database.yml

@@ -5,7 +5,7 @@
 users:
   ${AUTHELIA_ADMIN_USER}:
     displayname: ${AUTHELIA_ADMIN_USER}
-    password: "${AUTHELIA_ADMIN_PASSWORD_HASH}"
+    password: ${AUTHELIA_ADMIN_PASSWORD_HASH}
     email: ${AUTHELIA_ADMIN_EMAIL}
     groups:
       - admins