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/hooks/useRssiScanner.ts

@@ -0,0 +1,31 @@
+import { useEffect, useState } from 'react';
+import { rssiService, type WifiNetwork } from '@/services/rssi.service';
+import { useSettingsStore } from '@/stores/settingsStore';
+
+export function useRssiScanner(): { networks: WifiNetwork[]; isScanning: boolean } {
+  const enabled = useSettingsStore((state) => state.rssiScanEnabled);
+  const [networks, setNetworks] = useState<WifiNetwork[]>([]);
+  const [isScanning, setIsScanning] = useState(false);
+
+  useEffect(() => {
+    if (!enabled) {
+      rssiService.stopScanning();
+      setIsScanning(false);
+      return;
+    }
+
+    const unsubscribe = rssiService.subscribe((result) => {
+      setNetworks(result);
+    });
+    rssiService.startScanning(2000);
+    setIsScanning(true);
+
+    return () => {
+      unsubscribe();
+      rssiService.stopScanning();
+      setIsScanning(false);
+    };
+  }, [enabled]);
+
+  return { networks, isScanning };
+}