feat: app mobile React Native / Expo (v0.31.0)

Package mobile/ (Expo SDK 56, expo-router) réutilisant l'API backend :
Login (mdp+TOTP), Chat (+ TTS expo-speech), Review (approuver/refuser).
JWT en expo-secure-store, thème dark HUD, EXPO_PUBLIC_API_BASE. typecheck
vert. STT mobile reporté (lib native), TTS OK. Versions gérées par Expo.

Palier de risque : reversible (client mobile, API commune).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

mobile/app/index.tsx

@@ -0,0 +1,16 @@
+import { Redirect } from "expo-router";
+import { ActivityIndicator, View } from "react-native";
+import { useAuth } from "@/auth";
+import { C } from "@/theme";
+
+export default function Index() {
+  const { token, ready } = useAuth();
+  if (!ready) {
+    return (
+      <View style={{ flex: 1, justifyContent: "center", backgroundColor: C.bg }}>
+        <ActivityIndicator color={C.accent} />
+      </View>
+    );
+  }
+  return <Redirect href={token ? "/(tabs)/chat" : "/login"} />;
+}