feat: Phase 4 — Live, Vitals, Zones, MAT, Settings screens
LiveScreen: GaussianSplatWebView + gaussian-splats.html (Three.js 3D viz), LiveHUD
VitalsScreen: BreathingGauge, HeartRateGauge, MetricCard (Reanimated arcs)
ZonesScreen: FloorPlanSvg (SVG heatmap 20x20), ZoneLegend, useOccupancyGrid
MATScreen: MatWebView + mat-dashboard.html (pure-JS disaster response), AlertCard/List, SurvivorCounter
SettingsScreen: ServerUrlInput (URL validation + test), ThemePicker, RssiToggle
Verified: tsc 0 errors, jest passes