feat(lite): lite wallet foundation (inherited working-tree state)

Preserve the previously-uncommitted lite wallet implementation and related dev WIP
under version control:
- src/wallet/ lite services: client bridge, bridge runtime, connection, lifecycle,
  sync, gateway, result parsers, state mapper, artifact contract/resolver, refresh
  services, UI adapters, wallet_backend/capabilities. (Includes two small M1 fixes:
  lifecycle walletReady now parses the response; default chain name -> "main".)
- src/chat/ chat protocol; tests/fixtures/ (lite + hushchat); tools/hushchat_fixture_check.cpp;
  scripts/build-lite-backend-artifact.sh.
- Pre-existing modified app_network/security/wizard, network_refresh_service, sidebar,
  mining_tab, bootstrap dialog, and version headers captured as-is.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/wallet/wallet_backend.h

@@ -0,0 +1,93 @@
+// DragonX Wallet - ImGui Edition
+// Copyright 2024-2026 The Hush Developers
+// Released under the GPLv3
+
+#pragma once
+
+#include "wallet_capabilities.h"
+
+#include <cstdint>
+#include <optional>
+#include <string>
+#include <vector>
+
+namespace dragonx {
+namespace wallet {
+
+enum class WalletBackendState {
+    Unavailable,
+    Disconnected,
+    Connecting,
+    Syncing,
+    Ready,
+    Error
+};
+
+struct WalletBackendStatus {
+    WalletBackendState state = WalletBackendState::Unavailable;
+    std::string message;
+    std::optional<int> walletHeight;
+    std::optional<int> chainHeight;
+    double syncProgress = 0.0;
+};
+
+struct WalletBackendResult {
+    bool ok = false;
+    std::string error;
+};
+
+struct WalletOpenRequest {
+    std::string walletPath;
+    std::string serverUrl;
+    bool restoreFromSeed = false;
+};
+
+struct WalletSendRequest {
+    std::string fromAddress;
+    std::string toAddress;
+    double amount = 0.0;
+    double fee = 0.0;
+    std::string memo;
+};
+
+struct WalletSendResult {
+    bool accepted = false;
+    std::string txid;
+    std::string error;
+};
+
+class WalletBackend {
+public:
+    virtual ~WalletBackend() = default;
+
+    virtual WalletBackendKind kind() const = 0;
+    virtual WalletCapabilities capabilities() const = 0;
+    virtual WalletBackendStatus status() const = 0;
+};
+
+class FullNodeWalletBackend : public WalletBackend {
+public:
+    ~FullNodeWalletBackend() override = default;
+};
+
+class LiteWalletBackend : public WalletBackend {
+public:
+    ~LiteWalletBackend() override = default;
+
+    virtual WalletBackendResult setServer(const std::string& serverUrl) = 0;
+    virtual WalletBackendResult openWallet(const WalletOpenRequest& request) = 0;
+    virtual WalletBackendResult startSync() = 0;
+    virtual WalletBackendResult cancelSync() = 0;
+    virtual WalletSendResult sendTransaction(const WalletSendRequest& request) = 0;
+};
+
+class WalletBackendRouter {
+public:
+    virtual ~WalletBackendRouter() = default;
+
+    virtual WalletBackend& activeBackend() = 0;
+    virtual const WalletBackend& activeBackend() const = 0;
+};
+
+} // namespace wallet
+} // namespace dragonx