Add same-passphrase HD account derivation and grouping

[megabyte0x]

Summary

• adds atomic same-seed ZIP-32 software-account derivation, preserving the optional BIP-39 passphrase, reusing the lowest free account index, and returning opaque seed-family metadata
• groups matching software accounts into editable Wallet families in the desktop and mobile Accounts views while keeping hardware and unclassified accounts isolated
• extends the iOS regtest account-management journey to prove distinct address/UUID, secret preservation, shared seed family, group-name persistence, account actions, and passcode rotation
• fixes the mobile Add Account crash: deriving an account published router dependencies before navigation to Home, allowing GoRouter to rebuild the ephemeral customise route after CustomiseAccountArgs had been discarded

Closes #266.

Screenshots

Desktop	iOS

How to test

1. Install the iOS mobile build and unlock a software wallet.
2. Open Accounts -> Add account -> Get started -> Add Account.
3. Continue through customisation without entering a recovery phrase. The app must return to Home without a red error screen, with a distinct active unified address.
4. Open Manage accounts. The original and derived accounts should be in one Wallet family, with Current on that family.
5. Rename the family, leave and reopen Accounts, then relaunch and unlock; the family membership and name must persist.

Validation

• fvm flutter test --tags mobile --run-skipped --dart-define=VIZOR_FORM_FACTOR=mobile test/features/onboarding/mobile_welcome_screen_test.dart test/features/onboarding/mobile_customise_account_screen_test.dart (27 passed)
• SIMULATOR_UDID=E7E48642-4471-4C79-906B-037A4DDC6D09 scripts/e2e/flutter-ios-regtest-mobile-account-management.sh (passed)
• cd rust && cargo test (598 passed)