docs: reflect current state + tangible dream paths + teacher-corpus charter

Reconcile the vision docs with reality after the crypto-lever + autonomous-win work:
- README: rewrite Validated-so-far (zlib + full crypto family + ChaCha20/Salsa20
  model-unaided + Poly1305; 351 pairs, 95% model-authored) and the Roadmap with a
  Where-we-are (honest metrics) + a tangible path to the dream (fine-tune the corpus ->
  P1 fresh-library refusal-rate -> widen shape coverage -> ladder to ArduPilot).
- docs/CORPUS.md (NEW): charter for the teacher-corpus flywheel — how frontier-authored,
  tagged, oracle-verified worked-examples feed a fine-tune WITHOUT violating the
  never-hand-write-product rule; documents the loop closing on ChaCha20/Salsa20.
- docs/architecture.md: oracle shape catalog (9 levers) + reconcile the hand-tuned-ports
  note with the teacher corpus.
- docs/GROUNDING.md: 2026-07-29 addendum — teacher-corpus track distinct from product,
  the levers, the loop closing (harness-not-model, 4th confirmation), updated plan
  (fine-tune -> P1) so corpus growth does not crowd out the product metric.

Claude-Session: https://claude.ai/code/session_012BmSu5wWb15TMqN7u3jRnZ

Author: exx