Claude Session URL appended to commit messages and PR descriptions by default

Preflight Checklist 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-...