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/receive_tab.cpp

@@ -11,7 +11,9 @@
 #include "receive_tab.h"
 #include "send_tab.h"
 #include "../../app.h"
+#include "../../config/settings.h"
 #include "../../util/i18n.h"
+#include "../../util/platform.h"
 #include "../../config/version.h"
 #include "../../data/wallet_state.h"
 #include "../../ui/widgets/qr_code.h"
@@ -45,7 +47,7 @@ static std::string TrId(const char* key, const char* id) {
 // ============================================================================
 static int s_selected_address_idx = -1;
 static double s_request_amount = 0.0;
-static char s_request_memo[256] = "";
+static char s_request_memo[512] = "";
 static double s_request_usd_amount = 0.0;
 static bool s_request_usd_mode = false;
 static std::string s_cached_qr_data;
@@ -76,16 +78,9 @@ static std::string TruncateAddress(const std::string& addr, size_t maxLen = 40)
     return addr.substr(0, halfLen) + "..." + addr.substr(addr.length() - halfLen);
 }
 
-static void OpenExplorerURL(const std::string& address) {
-    std::string url = "https://explorer.dragonx.com/address/" + address;
-#ifdef _WIN32
-    std::string cmd = "start \"\" \"" + url + "\"";
-#elif __APPLE__
-    std::string cmd = "open \"" + url + "\"";
-#else
-    std::string cmd = "xdg-open \"" + url + "\"";
-#endif
-    system(cmd.c_str());
+static void OpenExplorerURL(App* app, const std::string& address) {
+    std::string url = app->settings()->getAddressExplorerUrl() + address;
+    dragonx::util::Platform::openUrl(url);
 }
 
 // ============================================================================
@@ -978,7 +973,7 @@ void RenderReceiveTab(App* app)
             ImGui::PushStyleVar(ImGuiStyleVar_FrameBorderSize, S.drawElement("tabs.receive", "explorer-btn-border-size").size);
             ImGui::PushStyleColor(ImGuiCol_Text, ImGui::ColorConvertU32ToFloat4(PrimaryLight()));
             if (TactileButton(TrId("explorer", "recv").c_str(), ImVec2(otherBtnW, btnH), S.resolveFont("button"))) {
-                OpenExplorerURL(selected.address);
+                OpenExplorerURL(app, selected.address);
             }
             ImGui::PopStyleVar(); // FrameBorderSize
             ImGui::PopStyleColor(4);