feat: add entitlements support to the React Native SDK

[dianaKhortiuk-frontegg]

What

Adds entitlements to the React Native SDK — on-device feature/permission gating — matching the native iOS/Android SDKs and the ionic-capacitor plugin (v2.1.1).

New JS API:

• loadEntitlements(forceRefresh = false): Promise<boolean>
• getFeatureEntitlement(key: string): Promise<Entitlement>
• getPermissionEntitlement(key: string): Promise<Entitlement>
• Entitlement = { isEntitled: boolean; justification?: string | null }

This is wiring, not a native change

The native SDKs this package already bundles ship the full feature, so no native version bump is needed:

• iOS FronteggSwift 1.3.10 — loadEntitlements, getFeatureEntitlements, getPermissionEntitlements
• Android frontegg-android-kotlin 1.3.34 — same

This PR only exposes them through the RN bridge + JS layer.

Changes

• Android (FronteggRNModule.kt) — three @ReactMethods calling FronteggAuth, serializing Entitlement → { isEntitled, justification }.
• iOS (FronteggRN.swift + FronteggRN.m) — matching @objc bridge methods.
• JS (FronteggNative.ts + index.tsx) — the three wrappers + the Entitlement type.
• Docs (docs/usage.md) — an Entitlements usage section.

Verification

• tsc --noEmit clean for src/; eslint clean on the changed files.
• Native compiles in CI (the iOS/Android E2E builds link the SDK into the example app).

Follow-ups (not in this PR)

• A demo button in the example app + an E2E case (the entitlements tests need a tenant with entitlements configured, so they'd follow the existing "skip without creds" pattern).

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