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/app.cpp

@@ -14,6 +14,7 @@
 #include "wallet/lite_wallet_controller.h"
 #include "wallet/lite_wallet_server_selection_adapter.h"
 #include "wallet/lite_rollout_policy.h"
+#include "wallet/lite_diagnostics.h"
 
 #include <cstdlib>  // std::getenv for the lite kill-switch env var
 #include <sodium.h>  // sodium_memzero for the lite unlock-passphrase buffer
@@ -29,6 +30,7 @@
 #include "ui/windows/mining_tab.h"
 #include "ui/windows/peers_tab.h"
 #include "ui/windows/network_tab.h"
+#include "ui/windows/lite_console_tab.h"
 #include "ui/windows/explorer_tab.h"
 #include "ui/windows/market_tab.h"
 #include "ui/windows/settings_window.h"
@@ -443,10 +445,11 @@ void App::rebuildLiteWallet(bool force)
     // does not block. The app's auto-open loop then reopens the wallet against the new server.
     if (!force && lite_wallet_ && lite_wallet_->walletOpen()) return;
 
+    const auto liteConn = wallet::liteConnectionSettingsFromAppSettings(*settings_);
+    wallet::liteLog(std::string(force ? "Lite controller rebuilt" : "Lite controller built") +
+                    " (preferred server: " + liteConn.stickyServerUrl + ")");
     lite_wallet_ = wallet::LiteWalletController::createLinked(
-        walletCapabilities(),
-        wallet::liteConnectionSettingsFromAppSettings(*settings_),
-        resolveLiteRolloutDecision(*settings_));
+        walletCapabilities(), liteConn, resolveLiteRolloutDecision(*settings_));
     lite_wallet_->setPersistCallback([this]() { settings_->save(); });
 
     // The new controller starts closed. Re-arm the one-shot auto-open so the next update()
@@ -1368,6 +1371,9 @@ void App::render()
         case ui::NavPage::LiteNetwork:
             ui::RenderLiteNetworkTab(this);
             break;
+        case ui::NavPage::LiteConsole:
+            ui::RenderLiteConsoleTab(this);
+            break;
         case ui::NavPage::Explorer:
             ui::RenderExplorerTab(this);
             break;