Add PR size warning workflow

[znrac137]

Summary

Adds an initial PR size warning workflow for the AutoAudit repository.

The workflow runs on pull requests to main and gives a warning when a PR becomes unusually large based on:

• changed files
• total line changes

Why warning only

This first version is warning-only rather than blocking so it stays low-risk and can be observed safely before any stricter enforcement is considered.

Thresholds used

• 30 changed files
• 500 total line changes

These were chosen as a starting point to flag unusually large PRs without creating too much noise for normal work.

Testing

I tested this workflow safely in my fork before opening this PR by:

• adding the workflow to .github/workflows/pr.size-warning.yml
• creating a separate test branch
• opening a pull request in the fork back into main
• triggering the warning with a large dummy test file

The workflow ran successfully and returned the expected PR size warning.

File added

• .github/workflows/pr.size-warning.yml