Add childrenPath to ParsedQrAccount for BC-UR keypath metadata

[Maskln]

paired with: https://github.com/AmbireTech/ambire-app/pull/7509

Summary

Adds an optional childrenPath field to ParsedQrAccount so QR wallet import can carry BC-UR crypto-hdkey children keypath metadata from the scanned payload.

When importing from Keycard Shell via QR, the UR payload encodes derivation in two parts:

• origin — parent xpub path (e.g. m/44'/60'/0')
• children — address discovery pattern (e.g. */* for BIP44 standard, * for Ledger Legacy)

Standard Ethereum and Ledger Legacy share the same origin path (m/44'/60'/0') but use different children patterns. Without exposing childrenPath, consumers cannot tell them apart and may derive the wrong address.

This is a type-only change in ambire-common. The parsing and derivation logic lives in ambire-app (companion PR on branch qr-code-based-wallets-derivation-paths).

Changes

• Add optional childrenPath?: string to ParsedQrAccount in src/interfaces/keystore.ts

Test plan

• Type-check passes (npm run type:check)
• ambire-app PR consuming this field builds and passes unit tests
• Keycard Shell Ledger Legacy QR import resolves to m/44'/60'/0'/0 (not m/44'/60'/0'/0/0)