feat: scaffold offline-first mobile app (RN+Expo, expo-sqlite)

Capa API tipada de los 8 endpoints, BD local espejo del bundle + outbox
(operaciones y media) + cursor de sync, motor runSync (PUSH /sync ->
PUSH /media -> PULL bundle?since) con idempotencia por uuid y last-write-wins,
mutaciones de alto nivel (write local + encolar), sesion con token en
SecureStore, conectividad NetInfo y UI minima (Login -> Proyectos -> Detalle).

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

src/net/connectivity.ts

@@ -0,0 +1,21 @@
+/**
+ * Estado de conectividad. Hook reactivo + comprobación puntual.
+ */
+import NetInfo from '@react-native-community/netinfo';
+import { useEffect, useState } from 'react';
+
+export function useIsOnline(): boolean {
+  const [online, setOnline] = useState(true);
+  useEffect(() => {
+    const unsubscribe = NetInfo.addEventListener((state) => {
+      setOnline(Boolean(state.isConnected && state.isInternetReachable !== false));
+    });
+    return unsubscribe;
+  }, []);
+  return online;
+}
+
+export async function isOnline(): Promise<boolean> {
+  const state = await NetInfo.fetch();
+  return Boolean(state.isConnected && state.isInternetReachable !== false);
+}