Adds ADR-0027 documenting the choice of `nemotron-3-super` (over
`gemma4:31b`) as the first model to onboard via `meta-trainer-bootstrap`
following the autonomy story validation today (PRs #53 + #54, Q-041).
Also reconciles the README index with reality:
- ADR-0026 was created in PR #40 but never added to the index → fixed
- ADRs 0009, 0013, 0018, 0019, 0021, 0022, 0024, 0025 had stale
Partially Implemented / Proposed statuses in the index — updated to
match what the ADR files themselves now say
- ADR-0023 status reflects Phase 1+2+3 Implemented
The index is now the source of truth for "where we are" — quick scan
confirms 0027 is the only Proposed ADR pending action.
