Agent Skills: PR Title and Description Generator

Generate or update GitHub Pull Request titles and descriptions from the actual code changes in the final state. Use whenever a PR is being opened or its title/description written — when the user says 'open a PR', 'create a PR', 'make/raise/submit a PR', 'update the PR', or mentions generating or writing PR descriptions, titles, or summaries. If no PR exists yet it pushes the branch and creates one; otherwise it updates the existing open PR. Analyzes the git diff to document what's actually in the code, not just commit history.