canary: add CPU-friendly smoke script; drop internal planning docs

- scripts/smoke_canary.py: load the Canary backend, transcribe a 16kHz clip,
  print word timestamps; runs on CPU (no GPU needed). Validates the backend
  end-to-end without a GPU.
- Remove docs/superpowers/ (internal implementation-planning notes) from the
  contribution so the PR carries only the backend, tests, and docs.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: fudai6