feat: Phase 3 — services, stores, navigation, design system

Services: ws.service, api.service, simulation.service, rssi.service (android+ios)
Stores: poseStore, settingsStore, matStore (Zustand)
Types: sensing, mat, api, navigation
Hooks: usePoseStream, useRssiScanner, useServerReachability
Theme: colors, typography, spacing, ThemeContext
Navigation: MainTabs (5 tabs), RootNavigator, types
Components: GaugeArc, SparklineChart, OccupancyGrid, StatusDot, ConnectionBanner, SignalBar, +more
Utils: ringBuffer, colorMap, formatters, urlValidator

Verified: tsc 0 errors, jest passes

mobile/src/components/ConnectionBanner.tsx

@@ -0,0 +1,70 @@
+import { StyleSheet, View } from 'react-native';
+import { ThemedText } from './ThemedText';
+
+type ConnectionState = 'connected' | 'simulated' | 'disconnected';
+
+type ConnectionBannerProps = {
+  status: ConnectionState;
+};
+
+const resolveState = (status: ConnectionState) => {
+  if (status === 'connected') {
+    return {
+      label: 'LIVE STREAM',
+      backgroundColor: '#0F6B2A',
+      textColor: '#E2FFEA',
+    };
+  }
+
+  if (status === 'disconnected') {
+    return {
+      label: 'DISCONNECTED',
+      backgroundColor: '#8A1E2A',
+      textColor: '#FFE3E7',
+    };
+  }
+
+  return {
+    label: 'SIMULATED DATA',
+    backgroundColor: '#9A5F0C',
+    textColor: '#FFF3E1',
+  };
+};
+
+export const ConnectionBanner = ({ status }: ConnectionBannerProps) => {
+  const state = resolveState(status);
+
+  return (
+    <View
+      style={[
+        styles.banner,
+        {
+          backgroundColor: state.backgroundColor,
+          borderBottomColor: state.textColor,
+        },
+      ]}
+    >
+      <ThemedText preset="labelMd" style={[styles.text, { color: state.textColor }]}>
+        {state.label}
+      </ThemedText>
+    </View>
+  );
+};
+
+const styles = StyleSheet.create({
+  banner: {
+    position: 'absolute',
+    left: 0,
+    right: 0,
+    top: 0,
+    zIndex: 100,
+    paddingVertical: 6,
+    borderBottomWidth: 2,
+    alignItems: 'center',
+    justifyContent: 'center',
+  },
+  text: {
+    letterSpacing: 2,
+    fontWeight: '700',
+  },
+});