Add NativeDeviceSignerKeyStorage with iOS/Android native bridge

[tomas-martins-crossmint]

Implements hardware-backed device signing for React Native / Expo wallets, rebased on wallets-v1 where the wallets-sdk device signer logic already lives.

Changes

@crossmint/expo-device-signer — new Expo native module exposing NativeDeviceSignerKeyStorage extends DeviceSignerKeyStorage:

• Android: P-256 key generation via KeyGenParameterSpec + SHA256withECDSA, metadata persisted in SharedPreferences
• iOS: delegates to CrossmintDeviceSigner CocoaPod (SecureEnclaveKeyStorage on device, KeychainDeviceSignerKeyStorage on simulator)
• hasKey(publicKeyBase64): Android checks SharedPreferences index; iOS maintains a UserDefaults index kept in sync across generate/delete calls
• Public keys encoded as uncompressed 65-byte P-256 points (0x04 || x || y) to match the format expected by createDeviceSigner

@crossmint/client-sdk-react-native-ui — wires up device signing:

• CrossmintWalletProvider gains a deviceSignerKeyStorage?: DeviceSignerKeyStorage prop
• Passed through to CrossmintWalletBaseProvider, which already handles device signer registration and re-registration

@crossmint/wallets-sdk — minor export addition:

• BiometricPolicy type is now exported from the package index

Usage

import { NativeDeviceSignerKeyStorage } from "@crossmint/expo-device-signer";

<CrossmintWalletProvider
    deviceSignerKeyStorage={new NativeDeviceSignerKeyStorage()}
>
    {children}
</CrossmintWalletProvider>

Notes

• iOS depends on CrossmintDeviceSigner CocoaPod from crossmint-swift-sdk — needs a tagged release before this can be merged
• Android is self-contained (Keystore + JCA, no external pod dependency)

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Latest commit: d966c04

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[github-actions]

🔥 Smoke Test Results

✅ Status: Passed

Statistics

• Total Tests: 5
• Passed: 5 ✅
• Failed: 0
• Skipped: 0
• Duration: 3.41 min

✅ All smoke tests passed!

All critical flows are working correctly.

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This is a non-blocking smoke test. Full regression tests run separately.