chore: remove pre-release planning artifacts

- Delete BOOTSTRAP.md and the planning/v1.1/ working notes that
  scaffolded the migration. The synthesized output already landed in
  src/, tests/, samples/, and docs/.
- Drop the four loose process artifacts left in the working tree
  (refactor-plan.md, refactor-prompt.md, breaking-changes.md,
  skipped.md). Never tracked; never relevant to consumers.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: nficano