Invert the global write toggle so writes are ENABLED by default and the user opts OUT, while keeping all other safety intact (per-call confirm=true dry-run preview and the on-disk audit log are unchanged). - writes.py: use a `writes_disabled` flag file instead of `writes_enabled`; `writes_enabled()` returns True unless the flag exists (env var still honored either way); `set_writes(False)` creates the flag, `set_writes(True)` removes it. Update user-facing notes. - tests: default is now ENABLED; adjust toggle/disabled tests (set disabled explicitly via set_writes(False) or FAMILIAR_ENABLE_WRITES=0). - README.md / CLAUDE.md: document writes are on by default, opt out via `familiar writes disable`. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>