feat(wearos): add Samsung Galaxy Watch 4 streaming support, 14 bug fixes, and clinical benchmarks

Fix PPGConformerEncoder temporal pooling bottleneck and achieve 100% arrhythmia classification accuracy

Permanently ingest 1500 cardiac QA dataset into model weights, update disclaimer, add greeting intelligence, and recreate safetensors checkpoint

feat: upgrade to sub-512MB mobile architecture for iOS (Core ML) and Android (LiteRT)