Review pull requests that only delete files - #34

This PR lets reviews proceed when a pull request only removes reviewable files: filtering happens before deleted files are classified, and the removed diff is included in the reviewer prompt within the diff budget. It adds guidance to look for remaining references, makes qualifying unplaceable findings and truncated deletion diffs withhold approval, and applies path-specific instructions to removed files. Tests cover filtering, deletion-only approvals, unplaceable findings, path instructions, and diff-budget truncation.