synthesize-init

Opt-in installer that sets /synthesize as the standing output default in an agent's directive files (CLAUDE.md, AGENTS.md, or equivalent), telling each future session to load it before its first nontrivial reply — a standing instruction, not deterministic enforcement; the live skill's best-effort boundary for later turns stays as it is. Shows the exact per-file diff first, backs the file up, writes between managed…