docs: convert remaining code examples from CommonJS to ESM

Summary

The quickstart guides and README were updated to use ESM imports in #2923. The remaining docs still use require() syntax and should be converted to import for consistency.

Files to update

English:

• docs/english/concepts/authenticating-oauth.md
• docs/english/concepts/custom-routes.md
• docs/english/concepts/deferring-initialization.md
• docs/english/concepts/error-handling.md
• docs/english/concepts/logging.md
• docs/english/concepts/message-listening.md
• docs/english/concepts/receiver.md
• docs/english/concepts/socket-mode.md
• docs/english/concepts/token-rotation.md
• docs/english/deployments/aws-lambda.md
• docs/english/tutorials/code-assistant.md

Japanese:

• docs/japanese/concepts/authenticating-oauth.md
• docs/japanese/concepts/custom-routes.md
• docs/japanese/concepts/deferring-initialization.md
• docs/japanese/concepts/error-handling.md
• docs/japanese/concepts/logging.md
• docs/japanese/concepts/message-listening.md
• docs/japanese/concepts/socket-mode.md
• docs/japanese/deployments/aws-lambda.md

Out of scope

• docs/english/legacy/steps-from-apps.md and docs/japanese/legacy/steps-from-apps.md — deprecated, no update needed.

Notes

• Most files are a straightforward require → import swap.
• Lambda deployment docs also use module.exports which should become export const handler.

Start with the English and Japanese Markdown files listed under concepts, deployments, and tutorials, and search them for require() and module.exports; use the ESM examples already applied in the quickstart guides and README as the reference. Convert the in-scope examples, including the Lambda handlers, while leaving both legacy/steps-from-apps.md files unchanged. Done means all listed docs use ESM consistently.