fix(ios): don't crash app init when Storefront region code is unavailable (#4291)

`getStorefrontRegionCode` rejects when `Storefront.current` is nil
(unsigned simulator, signed-out device, StoreKit not yet ready,
parental controls, etc.). The call sits in NativeAppService startup
before `prepareBooksDir`, so an unhandled rejection here aborts the
rest of init and surfaces as a top-level unhandledRejection in the
webview console.

Wrap the call in try/catch and treat failure as 'unknown region',
leaving `storefrontRegionCode` null so downstream region-gated
features degrade gracefully. Also guard against an empty resolve
shape with optional chaining on `res?.regionCode`.

apps/readest-app/src/services/nativeAppService.ts

@@ -492,9 +492,18 @@ export class NativeAppService extends BaseAppService {
     }
     if (this.isIOSApp) {
       this.isOnlineCatalogsAccessible = this.distChannel !== 'appstore';
-      const res = await getStorefrontRegionCode();
-      if (res.regionCode) {
-        this.storefrontRegionCode = res.regionCode;
+      try {
+        const res = await getStorefrontRegionCode();
+        if (res?.regionCode) {
+          this.storefrontRegionCode = res.regionCode;
+        }
+      } catch (err) {
+        // Storefront.current is nil on simulators without a signed-in
+        // App Store account, and may also fail on real devices with no
+        // StoreKit configuration. Treat as "unknown region" — we leave
+        // storefrontRegionCode as null and let downstream features that
+        // depend on region degrade gracefully.
+        console.warn('[nativeAppService] getStorefrontRegionCode failed:', err);
       }
     }
     await this.prepareBooksDir();