[FEATURE] Session URL appended to commit messages and PR descriptions by default — should be opt-in

Preflight Checklist I have searched existing requests and this feature hasn't been requested yet This is a single feature request (not multiple features) Problem Statement Every commit message and PR description created by Claude Code automatically includes a session URL at the bottom (e.g. https://claude.ai/code/session_...). There is no opt-in prompt, no warning, and no mention of it during onboarding. Users only discover it after it's already polluting their git history. Proposed Solution Make the session URL attribution opt-in — don't include it unless the user explicitly enables it. A one-time prompt during onboarding ("Would you like to include a link back to this Claude session in commit messages?") would be the ideal UX. Alternative Solutions Keep it opt-out but make the setting discoverable — show it during first commit with a "Don't add this again" option Remove it entirely and rely only on the existing Co-Authored-By: Claude trailer for attribution Priority Medium - Would be very helpful Feature Category Other Use Case Example A developer uses Claude Code to build a feature, commits the work, and opens a PR. Their teammates and open source contributors see https://claude.ai/code/session_... at the bottom of every commit and PR description. It looks unprofessional, clutters history, and the developer had no idea it was being added. Additional Context The attribution.commit: "" setting in .claude/settings.json can suppress it, but it's completely undiscovered A commit-msg git hook can also strip it, but it doesn't always fire reliably in remote/cloud environments