fix: reset keystore entries on wallet wipe

[ovitrif]

This PR fixes keystore cleanup during wallet wipe to prevent stale encryption keys from causing issues on subsequent wallet creation.

Description

When wiping a wallet, the keychain entries were cleared but the Android KeyStore encryption key remained. This could cause encryption/decryption failures if a new wallet reuses the same alias with different key material. The fix adds a deleteEncryptionKey() method to AndroidKeyStore and calls it during the wipe process.

Preview

N/A - No UI changes

QA Notes

1. Wallet wipe and restore

1. Create a new wallet and receive a small amount of sats
2. Wipe the wallet via Settings
3. Create a new wallet or restore from seed
4. Verify the wallet initializes without encryption errors
5. Confirm keychain operations (saving/reading mnemonic) work correctly

2. Regression - Normal wallet operations

1. Create a wallet and perform normal operations
2. Send/receive transactions
3. Close and reopen the app
4. Verify all wallet data persists correctly