feat(lite): Console tab with connection + open/create diagnostics

The lite variant had no visibility into why a wallet failed to open — just a
"disconnected" spinner. Add a lite-only Console tab (full-node keeps its RPC
console) that shows a live diagnostic log.

- LiteDiagnostics: a small thread-safe, bounded ring buffer (header-only). The
  controller writes to it from its background threads: each failover server
  attempt and result, wallet open/create/restore outcomes, sync start, and
  blocked-open reasons. The App logs controller (re)builds with the preferred
  server.
- lite_console_tab: a terminal-styled, read-only view of the log (newest at the
  bottom, error/success lines coloured) with Clear / Copy / Auto-scroll. Reachable
  even when the wallet is locked (it's diagnostics, no secrets). Registered as
  NavPage::LiteConsole, gated lite-only via WalletUiSurface::LiteConsole.

A unit test drives an open-with-failover and asserts the log records the
connection attempt and the successful open. Built clean for full-node, lite, and
Windows cross-compile.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/ui/windows/lite_console_tab.cpp

@@ -0,0 +1,98 @@
+// DragonX Wallet - ImGui Edition
+// Copyright 2024-2026 The Hush Developers
+// Released under the GPLv3
+
+#include "lite_console_tab.h"
+
+#include "../../app.h"
+#include "../../util/i18n.h"
+#include "../../wallet/lite_diagnostics.h"
+#include "../layout.h"
+#include "../material/type.h"
+#include "../material/colors.h"
+#include "imgui.h"
+
+#include <cstdint>
+#include <string>
+#include <vector>
+
+namespace dragonx {
+namespace ui {
+
+using namespace material;
+
+namespace {
+
+// Re-snapshot the (mutex-guarded) log only when it actually changes, not every frame.
+std::vector<std::string> s_lines;
+std::uint64_t s_cachedGeneration = static_cast<std::uint64_t>(-1);
+bool s_autoScroll = true;
+
+// Colour error/success lines for at-a-glance scanning (substring match on the messages the
+// controller emits). Anything else renders in the muted default colour.
+ImU32 lineColor(const std::string& line)
+{
+    const auto has = [&line](const char* s) { return line.find(s) != std::string::npos; };
+    if (has("failed") || has(" unreachable") || has("blocked") || has("could not") ||
+        has("Error") || has("error"))
+        return Error();
+    if (has(": connected") || has("opened") || has("wallet ready") || has("Ready"))
+        return Success();
+    return OnSurfaceMedium();
+}
+
+}  // namespace
+
+void RenderLiteConsoleTab(App* app)
+{
+    (void)app;
+    auto& diag = wallet::LiteDiagnostics::instance();
+    const std::uint64_t gen = diag.generation();
+    if (gen != s_cachedGeneration) {
+        s_lines = diag.snapshot();
+        s_cachedGeneration = gen;
+    }
+
+    // ── Header ──────────────────────────────────────────────────────────────────
+    Type().text(TypeStyle::H6, TR("lite_console_title"));
+    Type().textColored(TypeStyle::Caption, OnSurfaceMedium(), TR("lite_console_intro"));
+    ImGui::Spacing();
+
+    // ── Toolbar ─────────────────────────────────────────────────────────────────
+    if (ImGui::Button(TR("lite_console_clear"))) diag.clear();
+    ImGui::SameLine();
+    if (ImGui::Button(TR("lite_console_copy"))) {
+        std::string all;
+        for (const auto& l : s_lines) { all += l; all.push_back('\n'); }
+        ImGui::SetClipboardText(all.c_str());
+    }
+    ImGui::SameLine();
+    ImGui::Checkbox(TR("lite_console_autoscroll"), &s_autoScroll);
+    ImGui::Spacing();
+
+    // ── Log (terminal-styled scroll region) ─────────────────────────────────────
+    ImGui::PushStyleColor(ImGuiCol_ChildBg, IM_COL32(0, 0, 0, 90));
+    ImGui::BeginChild("##LiteConsoleLog", ImVec2(0, 0), true,
+                      ImGuiWindowFlags_HorizontalScrollbar);
+    ImGui::PushFont(Type().caption());
+    if (s_lines.empty()) {
+        ImGui::PushStyleColor(ImGuiCol_Text, OnSurfaceDisabled());
+        ImGui::TextUnformatted(TR("lite_console_empty"));
+        ImGui::PopStyleColor();
+    } else {
+        for (const auto& line : s_lines) {
+            ImGui::PushStyleColor(ImGuiCol_Text, lineColor(line));
+            ImGui::TextUnformatted(line.c_str());  // not format-interpreted — safe for any content
+            ImGui::PopStyleColor();
+        }
+    }
+    // Keep pinned to the newest line only while the user is already at the bottom.
+    if (s_autoScroll && ImGui::GetScrollY() >= ImGui::GetScrollMaxY())
+        ImGui::SetScrollHereY(1.0f);
+    ImGui::PopFont();
+    ImGui::EndChild();
+    ImGui::PopStyleColor();
+}
+
+}  // namespace ui
+}  // namespace dragonx

src/ui/windows/lite_console_tab.h

@@ -0,0 +1,18 @@
+// DragonX Wallet - ImGui Edition
+// Copyright 2024-2026 The Hush Developers
+// Released under the GPLv3
+//
+// Lite-wallet "Console" tab: a read-only, terminal-styled view of the lite diagnostics log
+// (server connection attempts, wallet open/create/restore, sync milestones, errors). Lite
+// builds only. See src/ui/windows/lite_console_tab.cpp.
+
+#pragma once
+
+namespace dragonx {
+class App;
+namespace ui {
+
+void RenderLiteConsoleTab(App* app);
+
+} // namespace ui
+} // namespace dragonx