Feature Parity 13: Legacy Wallet Migration Flow

[johnny9]

Summary

Add legacy wallet migration UX around walletLoader().migrateWallet.

Complexity

• L

Dependencies

• 10
• 12
• 02

Global Constraints

• All implementation lives under gui-qml/.
• No GUI runtime dependency on bitcoin/src/qt components. Reused logic must be moved/ported into gui-qml/.
• Do not change interfaces::Wallet or interfaces::Node in this version.
• Issue completion must satisfy DefinitionOfDone.md.

Scope

• Detect migration-eligible wallets.
• Add migration flow with passphrase prompt where needed.
• Display migration output, backup path, and follow-up actions.
• Handle partial migration and rollback messaging.

Acceptance Criteria (DoD-Aligned)

1. Eligible wallet can be migrated from UI.
2. Failure and partial warning conditions are clearly explained.
3. Migration backup location is shown to user.

Required Tests

• C++ unit tests: Unit tests for migration result mapping and edge-case handling.
• QML QTest: QTests for migration confirmation, password, and result states.
• Python E2E (qml/test/testbridge.h): E2E migration scenario with success + forced failure path checks.

Implementation Notes

• Document limitations in feature note because design coverage is currently not explicit.