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

fix(chat): resolve Q&A completion trigger, enhance RAG grounding, and add benchmark audit suite

Update model card and documentation for litert-community release

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)

Initial commit: MedGemma-Micro multimodal cardiology edge model with lifestyle management & legal waiver guard