feat(diagnostics): refresh-staleness badge on the Total Balance card (W6-2)

When the wallet is connected but the balance has quietly stopped refreshing — a busy
daemon can fail z_gettotalbalance without dropping the whole connection (only *both*
core RPCs failing 3x triggers a disconnect) — the old number sits on screen while the
node-status banner stays hidden. The Total Balance card now shows a small pill on its
status line ("Updated 2m ago", amber, escalating to red past 3 min) so the stale value
isn't silently trusted; hovering explains it and points at the node connection.

No refresh-path changes: WalletState::last_balance_update is already stamped only on a
successful fetch (network_refresh_service.cpp), so the badge reads it and computes age
against the same std::time clock via util::formatTimeAgoShort. The decision is a pure,
unit-tested helper (ui/staleness_badge.h::evaluateStalenessBadge, 45s/180s thresholds)
gated on connected so it never contradicts the banner.

Closes P2 (5/5). Build-clean; ctest 1/1 (adds testStalenessBadge).

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

src/ui/staleness_badge.h

@@ -0,0 +1,48 @@
+#pragma once
+
+#include <cstdint>
+
+// Refresh-staleness badge (finding W6-2). The wallet stamps WalletState::last_balance_update only on
+// a *successful* balance fetch (see services/network_refresh_service.cpp), so a busy daemon that fails
+// z_gettotalbalance without dropping the whole connection leaves the old balance on screen with a
+// frozen timestamp — and the node-status banner (which only fires on a full disconnect) stays hidden.
+// This badge is the surface that reflects that "connected but the number may be out of date" state.
+//
+// The decision is a pure function of (last-success timestamp, now, connected) so it is unit-testable;
+// balance_tab.cpp draws the pill. Both use the same std::time(nullptr) wall-clock the refresh path
+// stamps with, so age = now - last_update is consistent.
+namespace dragonx::ui {
+
+enum class StalenessSeverity {
+    Warning,  // amber — noticeably behind
+    Error,    // red — very stale, something is likely wrong
+};
+
+struct StalenessBadge {
+    bool              show        = false;
+    StalenessSeverity severity    = StalenessSeverity::Warning;
+    std::int64_t      seconds_old = 0;
+};
+
+// Balance refreshes every ~2s on the Overview profile (and ~10s while syncing), so tens of seconds
+// with no successful update means refreshes are failing, not merely slow.
+inline constexpr std::int64_t kStaleAfterSeconds     = 45;
+inline constexpr std::int64_t kVeryStaleAfterSeconds = 180;
+
+inline StalenessBadge evaluateStalenessBadge(std::int64_t last_update, std::int64_t now, bool connected) {
+    StalenessBadge b;
+    // Offline is the node-status banner's job; don't double up. A zero stamp means "never updated
+    // this session" (fresh start) or "reset on disconnect" — nothing to be stale about yet.
+    if (!connected || last_update <= 0) return b;
+
+    std::int64_t age = now - last_update;
+    if (age < 0) age = 0;  // clock skew guard
+    if (age < kStaleAfterSeconds) return b;
+
+    b.show        = true;
+    b.seconds_old = age;
+    b.severity    = (age >= kVeryStaleAfterSeconds) ? StalenessSeverity::Error : StalenessSeverity::Warning;
+    return b;
+}
+
+}  // namespace dragonx::ui

src/ui/windows/balance_tab.cpp

@@ -26,6 +26,7 @@
 #include "../effects/imgui_acrylic.h"
 #include "../sidebar.h"
 #include "../notifications.h"
+#include "../staleness_badge.h"
 #include "../../embedded/IconsMaterialDesign.h"
 #include "imgui.h"
 #include <toml++/toml.hpp>
@@ -421,6 +422,25 @@ static void RenderBalanceClassic(App* app)
                 dl->AddText(capFont, capFont->LegacySize,
                             ImVec2(cx + 12 * dp, cy),
                             WithAlpha(Success(), 200), buf);
+            } else {
+                // Refresh-staleness badge (W6-2): connected, not syncing/mining, but the balance
+                // hasn't refreshed in a while (a busy daemon can fail z_gettotalbalance without
+                // dropping the whole connection). The node banner only covers full disconnects, so
+                // this pill is the sole signal that the shown number may be out of date.
+                StalenessBadge badge = evaluateStalenessBadge(
+                    state.last_balance_update, std::time(nullptr), state.connected);
+                if (badge.show) {
+                    const bool err = (badge.severity == StalenessSeverity::Error);
+                    ImU32 fg = err ? Error() : Warning();
+                    ImU32 bg = WithAlpha(fg, 38);
+                    ImU32 bd = WithAlpha(fg, 90);
+                    snprintf(buf, sizeof(buf), "%s %s",
+                             TR("data_stale_prefix"), timeAgo(state.last_balance_update).c_str());
+                    ImVec2 pillSz = DrawPill(dl, ImVec2(cx, cy), buf, capFont, fg, bg, bd);
+                    // Hover → explain what stale means and how old the data actually is.
+                    if (material::IsRectHovered(ImVec2(cx, cy), ImVec2(cx + pillSz.x, cy + pillSz.y)))
+                        Tooltip("%s", TR("data_stale_tooltip"));
+                }
             }
 
             // Hover glow

src/util/i18n.cpp

@@ -1315,6 +1315,11 @@ void I18n::loadBuiltinEnglish()
         strings_["node_banner_lite_open_failed"] = "Couldn't open your wallet";
         strings_["node_banner_reconnect"] = "Reconnect";
         strings_["node_banner_restart"] = "Restart node";
+        // Refresh-staleness badge (W6-2) on the Total Balance card.
+        strings_["data_stale_prefix"] = "Updated";
+        strings_["data_stale_tooltip"] =
+            "Balance may be out of date — the wallet hasn't received a fresh update recently. "
+            "Check your node connection.";
         strings_["daemon_port_busy_warn"] =
             "Port " DRAGONX_DEFAULT_RPC_PORT " is in use but isn't responding as a DragonX node. "
             "Close the program using it (or free the port), then restart — the wallet can't start "