feat: make GitHub query limits configurable via env

[ShashwatUpadhayay]

Make GitHub query limits configurable through environment variables:

• GITHUB_REPO_COUNT
• GITHUB_PR_COUNT
• GITHUB_ISSUE_COUNT
• GITHUB_DISCUSSION_COUNT
• Add parsing and validation with sensible defaults and upper bounds
• Replace hardcoded query limits with runtime configuration
• Document the new environment variables
• Add unit tests for parsing and validation logic

Testing

• Verified default values are used when environment variables are missing or invalid
• Verified valid values are parsed correctly
• Verified oversized values are clamped to the configured maximum
• Ran the test suite successfully

Close #160

[vercel]

@ShashwatUpadhayay is attempting to deploy a commit to the osama's projects Team on Vercel.

A member of the Team first needs to authorize it.

[github-actions]

Thank you for the pull request! ✅

A maintainer will review this soon. Please be patient while we take a look. 🙌

[O2sa]

Close the other PR and close the relative issue by adding this to the PR description:

Close #ISSUE_ID

And I will be happy to accept this PR.

[ShashwatUpadhayay]

You may merge this PR now as I have closed the earlier one and My apologies for all the inconvenience caused :)

[O2sa]

Another time add the close command in the PR that's will be merged and the issue will be closed automatically, like how I did here: #167 (comment)

And don't forget to star the repo :)