fix: improve bpm reliability

fix: stop locking focus to keep iphone autofocus active

perf: optimize signal processing pipeline and cleanup frontend

perf: optimize shader background rendering

feat: migrate rPPG pipeline to FaceLandmarker and 5-method adaptive extraction

fix: move ROI from buggy forehead to cheeks with correct centering

fix: improve BPM accuracy with first-peak autocorrelation and bandpass fix

feat: add measurement UI components and measure page with phase machine

feat: add webcam feed with face detection and RGB extraction

feat: redesign landing page with shader bg and animated CTA