Fix PR Review Comments

Fetch review comments from a GitHub PR and apply fixes to the local codebase.

Current PR context

!gh pr view --json number,url,headRefName 2>/dev/null || echo "NO_PR_FOUND"

Step 1: Identify the PR

If the user provided a PR number as $ARGUMENTS, use that instead of the auto-detected PR above.

If no PR is found (output shows NO_PR_FOUND and no argument was given), stop and tell the user:

• There is no open PR for the current branch
• They need to either push and create a PR first, or provide a PR number

Step 2: Verify gh CLI is available