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/balance_tab.cpp

@@ -326,7 +326,7 @@ static void RenderBalanceClassic(App* app)
     // Lerp displayed balances toward actual values
     {
         float dt = ImGui::GetIO().DeltaTime;
-        float speed = kBalanceLerpSpeed;
+        float speed = (app->settings() && app->settings()->getReduceMotion()) ? 999.0f : kBalanceLerpSpeed;
         auto lerp = [](double& disp, double target, float dt, float spd) {
             double diff = target - disp;
             if (std::abs(diff) < 1e-9) { disp = target; return; }
@@ -1278,7 +1278,7 @@ static void UpdateBalanceLerp(App* app) {
     const float kBalanceLerpSpeed = S.drawElement("tabs.balance", "balance-lerp-speed").sizeOr(8.0f);
     const auto& state = app->state();
     float dt = ImGui::GetIO().DeltaTime;
-    float speed = kBalanceLerpSpeed;
+    float speed = (app->settings() && app->settings()->getReduceMotion()) ? 999.0f : kBalanceLerpSpeed;
     auto lerp = [](double& disp, double target, float dt, float spd) {
         double diff = target - disp;
         if (std::abs(diff) < 1e-9) { disp = target; return; }