feat: ThemeContext + Settings tabs (Interface / App / Sync)

- ThemeContext: dynamic palette (Default/Giro/Tour/Vuelta), font size
  (small/medium/large), bold labels — all persisted to AsyncStorage
- Settings: three top tabs; Interface tab has palette picker + font
  size pills + bold labels toggle; App tab has km notifications;
  Sync tab has bincio instance login + autarchive placeholder
- RecordingScreen: stat labels now use theme accent colour and scale
  with fontSize; font weight follows boldLabels setting
- All accent/accentDim usages migrated from static colors to useTheme()

App.tsx

@@ -2,17 +2,17 @@ import { useEffect } from 'react';
 import { StatusBar } from 'expo-status-bar';
 import * as Notifications from 'expo-notifications';
 import { GestureHandlerRootView } from 'react-native-gesture-handler';
+import { ThemeProvider } from './src/ThemeContext';
 import { AppNavigator } from './src/navigation/AppNavigator';
 import { requestNotificationPermissions } from './src/services/gps';
 import { promptBatteryOptimizationIfNeeded } from './src/services/batteryOptimization';
 
-// Show notifications even when the app is in the foreground (iOS suppresses by default)
 Notifications.setNotificationHandler({
   handleNotification: async () => ({
     shouldShowBanner: true,
-    shouldShowList: true,
-    shouldPlaySound: true,
-    shouldSetBadge: false,
+    shouldShowList:   true,
+    shouldPlaySound:  true,
+    shouldSetBadge:   false,
   }),
 });
 
@@ -24,8 +24,10 @@ export default function App() {
 
   return (
     <GestureHandlerRootView style={{ flex: 1 }}>
-      <StatusBar style="light" />
-      <AppNavigator />
+      <ThemeProvider>
+        <StatusBar style="light" />
+        <AppNavigator />
+      </ThemeProvider>
     </GestureHandlerRootView>
   );
 }