Feature request(GitHub App): Specify label name to be reviewed in .env

Purpose

As per Github Actions version, it would be convenient if you can specify the label name to be reviewed in GitHub App version.

Suggestion

Here's my implementation suggestion.

• add label name to .env
  add label name such as TARGET_LABEL to .env.
  https://github.com/anc95/ChatGPT-CodeReview/blob/main/.env.example

• add a label check in bot.ts
  If TARGET_LABEL is specified in .env, check if the label is attached.

      const target_label = process.env.TARGET_LABEL
      if (target_label && pull_request.labels.every(label => label.name !== target_label)) {
        return "no target label attached"
      }

https://github.com/anc95/ChatGPT-CodeReview/blob/8833ed9067356702bde83caaedee0627a5ca3de4/src/bot.ts#L61

I also tried to make a PR, but npm test doesn't work for my environment. (Windows / WSL2)

Start with .env.example and the label-handling logic in src/bot.ts around the linked line. Check how existing environment variables are read and run npm test if the local setup permits. Done means an optional TARGET_LABEL setting prevents review when the pull request lacks that label, while preserving current behavior when it is unset.