Each ml/features/*.py now declares freshness, source, and fallback per
feature. ProfileFeature gains ttl_sec (mirrored from registry.ts),
freshness="batched", source, and fallback. context.py adds
ContextFeatureSpec + CONTEXT_FEATURES for the three JIT features
(hour_of_day, day_of_week, tasks). CI test parses ttlSec from registry.ts
to catch drift. ml/README updated with split JIT/batched feature contract.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>