feat(wallet): complete SSSS round-trip with delete and restore

Delete Wallet feature:
- Add showDeleteConfirmation state to WalletPanelState
- Add WalletDeleteConfirmationDialog composable with warning
- Non-dismissible dialog with clear warning about backup
- Wire DeleteWallet/ConfirmDeleteWallet/CancelDeleteWallet events
- Call keyStorage.deleteWallet() and clear wallet state on confirm
- Panel shows setup screen after deletion

Restore from SSSS feature:
- Add hasBackupWithoutKey() to WalletBackupService for checking backup existence
- Uses raw Matrix account data API to check if secret key exists
- Add RESTORE_FROM_CLOUD step to SetupStep enum
- Check for cloud backup on setup init (non-blocking)
- Show "Restore from Matrix Backup" button when backup exists
- Add recovery key input flow for cloud restore
- Restore decrypts mnemonic from SSSS and imports wallet

Both features enable complete wallet backup/restore round-trip via Matrix SSSS.

features/wallet/api/src/main/kotlin/io/element/android/features/wallet/api/backup/WalletBackupService.kt

@@ -46,4 +46,14 @@ interface WalletBackupService {
      * @return True if a backup exists, false otherwise
      */
     suspend fun hasBackup(recoveryKey: String): Result<Boolean>
+
+    /**
+     * Check if a wallet backup exists in account data WITHOUT decrypting.
+     *
+     * This checks the raw Matrix account data to see if the secret key exists,
+     * without needing the recovery key. Useful for UI to show restore option.
+     *
+     * @return True if the account data key exists, false otherwise
+     */
+    suspend fun hasBackupWithoutKey(): Result<Boolean>
 }