feat(foundry): lyric-aware vocal sampler (engine/vox.py) — phrase-level, hook-ranked, loop-capable vox one-shots

PROBLEM. The Foundry's vocal path (loops.analyze_chops) cuts vocals blind to what
is sung — onset→onset slices scored on seam/zc mechanics. But a vocal one-shot's
value to a livecoder IS the lyric. The freshly-shipped superfreak dub kit had four
tiny 0.35-0.65s onset chops (03-06) with no idea they sat on top of some of the most
iconic lyrics in funk ("she's a super freak", "kinky girl", "the kind you read about").

APPROACH. engine/vox.py: transcribe → phrase-segment → iconicity-rank → cut → grade →
lyric-name, DRY-reusing grade.py sub-scorers and naming.py convention.
 - transcribe: whisper word-level timestamps, shelled out like separate.py→demucs,
   cached at workspace/vox_transcript.json so re-runs are instant. Model escalates
   small→medium empirically when the known hooks don't surface (small garbled the
   patois delivery; medium recovers the real lyrics).
 - segment: group words on inter-word gaps (>=0.45s), cap 6s, split over-long phrases
   at their widest interior gap; keep per-phrase avg ASR confidence.
 - iconicity: feature-engineered rank = repetition (normalized phrase text + content
   n-grams recurring across the track — hooks repeat) + hook keywords (title-derived
   or --hooks) + clarity (ASR prob) + energy (RMS vs stem median) + duration sweet-spot.
 - cut: pre-pad + post-pad (clamped to next phrase), zero-crossing snap both edges,
   3-10ms fades so edge samples are ~0 regardless of where the snap landed; as-cut level.
 - kit-level loopability: report each phrase's duration in BEATS at the kit BPM; flag
   loop-capable phrases (within ±3% of a 1/2/4-bar multiple) and emit a bar-quantized
   _loop variant (tail pulled to the exact beat grid, still zc-snapped) for the best
   hooks, so a vocal can loopAt alongside instrument loops.
 - name: NN_vox_<lyricslug> (naming.lint-clean), dedup identical texts (best-graded
   instance, up to 2 takes of THE hook).

VALIDATION. 17 new mocked-transcription tests (whisper never runs in tests): gap
segmentation, over-long split, iconicity repetition-beats-oneoff + hook-keyword boost,
beat/loop annotation, cut edges ~0 after zc+fade, next-start clamp, exact-beat loop
variant, lyric-slug + lint contract. Full suite 60->77 green. Applied to the superfreak
stem: medium transcript contains every iconic line; shipped 6 curated vox files (S/B
tier) replacing the 4 blind chops, incl. one 2-bar (8.00-beat) loop variant. All
re-graded on disk: no clip (peaks <0.8), no DC (<2e-4), edges exactly 0.0.