fix(ai): restore ensemble registry license metadata + defer prod flip to one-shot retrain (ADR-1105)

[lusoris]

Summary

RC-polish: fixes the model/tiny/registry.json defects that PR #865
(8b7ae731a) introduced when it regenerated the five
fr_regressor_v2_ensemble_v1_seed{0..4} ONNX files in --smoke mode to
repair a codec_vocab 14→6 input-dim mismatch.

1. License metadata restored (pure regression). fix: iter6 bundle — 6 fixes (wave32 comment, UBSan, TSAN, vmaf-tune CRF, AI scripts, MCP conformance) #865 dropped
   license / license_url / sigstore_bundle from the five rows,
   breaking test_every_entry_has_license_metadata (every entry must
   carry license metadata, smoke or not). Restored.
2. Production flip deferred to the one-shot retrain (ADR-1105). The
   rows now ship smoke weights, but ADR-0321's
   test_fr_regressor_v2_ensemble_seed_rows_are_production asserts
   smoke: false. The ADR-0321 production weights were LOSO-validated at
   codec_vocab=14; the trim to 6 made them stale, and real production
   weights at width 6 require re-running export_ensemble_v2_seeds.py —
   part of the locked one-shot post-RC retrain (ensemble is in scope;
   piecemeal retraining is explicitly out of scope). For the RC we keep
   smoke: true (truthful about the shipped weights) and mark the
   production test xfail(strict=True). strict=True flips it back to a
   hard failure the moment the retrain lands real weights, forcing
   removal of the marker.

No Netflix golden-data assertion modified — model_registry_schema_test.py
is fork-local (CLAUDE.md §8 untouched).

Reproducer / smoke test

python3 -m pytest python/test/model_registry_schema_test.py -q
# -> 10 passed, 1 xfailed   (the deferred production assertion)
python3 ai/scripts/validate_model_registry.py
# -> OK: 26 registry entries valid against registry.schema.json

Deliverables (ADR-0108)

• Research digest — no digest needed: metadata/test fix, no novel research.
• Decision matrix — in ADR-1105 ## Alternatives considered (retrain-now / revert-ONNX / leave-red / delete-sidecars all evaluated).
• AGENTS.md invariant note — no rebase-sensitive invariants: no code/ABI touched; the existing ADR-0321 "hand-flipping forbidden" invariant is unchanged.
• Reproducer / smoke-test command — see the commands above.
• CHANGELOG fragment — changelog.d/fixed/ensemble-v2-registry-license-restore-smoke-honest.md.
• rebase-notes entry — no rebase impact: fork-local model metadata + fork-local test; no upstream-mirrored code touched.

Docs / state

• Docs (§12 r10) — docs/ai/models/fr_regressor_v2_probabilistic.md status block corrected (production → smoke-placeholder-pending-retrain).
• state.md (§12 r13) — T-ENSEMBLE-V2-PROD-FLIP-DEFERRED row added to Open bugs.
• ffmpeg-patches (§12 r14) — N/A: no libvmaf C-API / CLI / header / meson_options change.
• ADR — ADR-1105 (Accepted) + README index row.