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/stores/settingsStore.ts

@@ -0,0 +1,47 @@
+import AsyncStorage from '@react-native-async-storage/async-storage';
+import { create } from 'zustand';
+import { createJSONStorage, persist } from 'zustand/middleware';
+
+export type Theme = 'light' | 'dark' | 'system';
+
+export interface SettingsState {
+  serverUrl: string;
+  rssiScanEnabled: boolean;
+  theme: Theme;
+  alertSoundEnabled: boolean;
+  setServerUrl: (url: string) => void;
+  setRssiScanEnabled: (value: boolean) => void;
+  setTheme: (theme: Theme) => void;
+  setAlertSoundEnabled: (value: boolean) => void;
+}
+
+export const useSettingsStore = create<SettingsState>()(
+  persist(
+    (set) => ({
+      serverUrl: 'http://192.168.1.100:8080',
+      rssiScanEnabled: false,
+      theme: 'system',
+      alertSoundEnabled: true,
+
+      setServerUrl: (url) => {
+        set({ serverUrl: url });
+      },
+
+      setRssiScanEnabled: (value) => {
+        set({ rssiScanEnabled: value });
+      },
+
+      setTheme: (theme) => {
+        set({ theme });
+      },
+
+      setAlertSoundEnabled: (value) => {
+        set({ alertSoundEnabled: value });
+      },
+    }),
+    {
+      name: 'wifi-densepose-settings',
+      storage: createJSONStorage(() => AsyncStorage),
+    },
+  ),
+);