v2.1.0 — Brain bootstraps into native memory

Brain 2.1 — bootstraps into Claude Code's native memory.

• install.sh now registers the brain-nudge Stop hook (merge, not overwrite)
• brain-bootstrap: on-demand native→brain redirect (non-destructive, backs up first)
• /project-brain init seeds the redirect for the current workspace
• README/hook wording fix (turn-end + throttle)

Full notes in CHANGELOG.