Fix nested passphrase wallet display and backups

[scgbckbone]

Summary

BIP-39 passphrase wallets are represented internally as temporary extended private keys. Because a passphrase can be applied to a word-based temporary seed, the persistent master seed is not necessarily the passphrase wallet’s parent.

Update secret display and backup workflows to consistently use the wallet currently in effect:

• Show the effective XPRV in View Seed Words when a BIP-39 passphrase is active, without displaying the parent seed words or passphrase.
• Make Backup System, Clone Coldcard, and Key Teleport’s Full COLDCARD Backup capture the active temporary or passphrase wallet.
• Warn before exporting when a temporary seed or passphrase wallet is active.
• Remove the choice between master and passphrase-wallet backups, since that choice cannot correctly represent passphrases applied to temporary seeds.
• Simplify related temporary-secret bypass and settings-switching logic.
• Correct related passphrase restoration and temporary-to-master messaging.

The backup file format is unchanged. Passphrase-wallet backups contain the effective XPRV, not the parent seed words or passphrase.

[scgbckbone]

OK by KIMI3