v1.2.0: UX audit — security fixes, accessibility, and polish

Security (P0):
- Fix sidebar remaining interactive behind lock screen
- Extend auto-lock idle detection to include active widget interactions
- Distinguish missing PIN vault from wrong PIN; auto-switch to passphrase

Blocking UX (P1):
- Add 15s timeout for encryption state check to prevent indefinite loading
- Show restart reason in loading overlay after wallet encryption
- Add Force Quit button on shutdown screen after 10s
- Warn user if embedded daemon fails to start during wizard completion

Polish (P2):
- Use configured explorer URL in Receive tab instead of hardcoded URL
- Increase request memo buffer from 256 to 512 bytes to match Send tab
- Extend notification duration to 5s for critical operations (tx sent,
  wallet encrypted, key import, backup, export)
- Add Reduce Motion accessibility setting (disables page fade + balance lerp)
- Show estimated remaining time during mining thread benchmark
- Add staleness indicator to market price data (warning after 5 min)

New i18n keys: incorrect_pin, incorrect_passphrase, pin_not_set,
restarting_after_encryption, force_quit, reduce_motion, tt_reduce_motion,
ago, wizard_daemon_start_failed

src/ui/windows/market_tab.cpp

@@ -237,6 +237,26 @@ void RenderMarketTab(App* app)
                             ImVec2(centerX - valSz.x * 0.5f, valY), stats[i].valueCol, stats[i].value.c_str());
             }
 
+            // ---- STALENESS INDICATOR ----
+            {
+                auto fetchTime = market.last_fetch_time;
+                if (fetchTime.time_since_epoch().count() > 0) {
+                    auto elapsed = std::chrono::steady_clock::now() - fetchTime;
+                    int ageSecs = (int)std::chrono::duration_cast<std::chrono::seconds>(elapsed).count();
+                    bool stale = ageSecs > 300; // 5 minutes
+                    if (ageSecs < 60)
+                        snprintf(buf, sizeof(buf), "%s %ds %s", stale ? ICON_MD_WARNING : "", ageSecs, TR("ago"));
+                    else
+                        snprintf(buf, sizeof(buf), "%s %dm %s", stale ? ICON_MD_WARNING : "", ageSecs / 60, TR("ago"));
+                    ImFont* staleFont = capFont;
+                    ImU32 staleCol = stale ? Warning() : WithAlpha(OnSurface(), 100);
+                    float staleY = statsY + ovFont->LegacySize + Layout::spacingXs() + sub1->LegacySize + Layout::spacingSm();
+                    ImVec2 staleSz = staleFont->CalcTextSizeA(staleFont->LegacySize, FLT_MAX, 0, buf);
+                    dl->AddText(staleFont, staleFont->LegacySize,
+                                ImVec2(cardMin.x + Layout::spacingLg(), staleY), staleCol, buf);
+                }
+            }
+
             // ---- TRADE BUTTON (top-right of card) ----
             if (!currentExchange.pairs.empty()) {
                 const char* pairName = currentExchange.pairs[s_pair_idx].displayName.c_str();