feat(wallet): add reusable wallet modules

Add program-neutral wallet access, a stable account model, reusable QML controls, transaction confirmation, submitted-transaction presentation, and isolated contract tests.\n\nRefs #227

apps/shared/wallet/src/WalletProvider.cpp

@@ -0,0 +1,26 @@
+#include "WalletProvider.h"
+
+QString walletFailureCode(WalletFailure failure)
+{
+    switch (failure) {
+    case WalletFailure::None:
+        return {};
+    case WalletFailure::WalletMissing:
+        return QStringLiteral("wallet_missing");
+    case WalletFailure::WalletUnavailable:
+        return QStringLiteral("wallet_unavailable");
+    case WalletFailure::OpenFailed:
+        return QStringLiteral("open_failed");
+    case WalletFailure::CreateFailed:
+        return QStringLiteral("create_failed");
+    case WalletFailure::SaveFailed:
+        return QStringLiteral("save_failed");
+    case WalletFailure::ReadFailed:
+        return QStringLiteral("read_failed");
+    case WalletFailure::InvalidRequest:
+        return QStringLiteral("invalid_request");
+    case WalletFailure::SubmissionFailed:
+        return QStringLiteral("submission_failed");
+    }
+    return QStringLiteral("wallet_unavailable");
+}