refactor(audit): batch 4 — UI design-system helpers + i18n

Mechanical, behavior-preserving consolidations from the audit. Rendering
extractions were kept byte-equivalent; sites that couldn't be made identical
were left as-is (noted below).

Shared helpers:
- util::truncateMiddle(s,maxLen) / (s,front,back) in text_format.h — replaces
  6 file-local middle-ellipsis truncators + several inline substr sites
  (send/receive/transactions/balance_recent_tx/explorer + app.cpp + 3 dialogs).
  Carries the maxLen<=3 guard, fixing the latent unsigned-underflow copies.
- material::LoadingDots() in draw_helpers.h — one animated-ellipsis source for
  8 copy-pasted spinner sites (identical GetTime()*3 phase preserved).
- Reuse the existing FormatHashrate() in explorer_tab + peers_tab (dropped two
  inline hashrate ladders).
- material::DrawButtonGlassOverlay() — the glass-fill/rim/tactile overlay block
  shared by TactileButton / TactileSmallButton / schema TactileButton.
- material::CollapsibleHeader() — the invisible-button + label + chevron idiom
  (3 of 5 settings_page sites; RPC/Debug headers skipped — non-identical).
- material::GlassCardScope (RAII) — the ChannelsSplit/Indent/DrawGlassPanel/
  ChannelsMerge card scaffold (5 settings_page cards; About/send/receive skipped
  — different padding / logo interleaving).
- material::DialogWarningHeader()/DialogConfirmFooter() — warning header +
  50/50 Cancel/danger footer across the confirm dialogs; button height moved
  from a hardcoded 40px into ui.toml (components.overlay-dialog.confirm-btn-height).
- File-local enterLowSpec()/exitLowSpec() collapse the 3 low-spec snapshot copies.

i18n: wrapped hardcoded English in the shared balance render paths and the
whole Lite lifecycle/security section in TR(), with English defaults added to
loadBuiltinEnglish() (res/lang/*.json left for the translation tooling — TR
falls back to English, so output is unchanged).

Full-node + Lite build clean; ctest 1/1; hygiene clean. These are rendering
changes — the Settings page (cards/headers/confirm dialogs), all tactile
buttons, and the Lite settings section warrant a screenshot check.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/ui/windows/settings_window.cpp

@@ -487,12 +487,8 @@ void RenderSettingsWindow(App* app, bool* p_open)
             // Confirmation dialog
             if (s_confirm_clear_ztx) {
                 if (material::BeginOverlayDialog(TR("confirm_clear_ztx_title"), &s_confirm_clear_ztx, 480.0f, 0.94f)) {
-                    ImGui::PushFont(material::Type().iconLarge());
-                    ImGui::TextColored(ImVec4(1.0f, 0.6f, 0.0f, 1.0f), ICON_MD_WARNING);
-                    ImGui::PopFont();
-                    ImGui::SameLine();
-                    ImGui::TextColored(ImVec4(1.0f, 0.6f, 0.0f, 1.0f), "%s", TR("warning"));
-                    
+                    material::DialogWarningHeader(TR("warning"), ImVec4(1.0f, 0.6f, 0.0f, 1.0f));
+
                     ImGui::Spacing();
                     ImGui::TextWrapped("%s", TR("confirm_clear_ztx_warning1"));
                     ImGui::Spacing();
@@ -500,15 +496,14 @@ void RenderSettingsWindow(App* app, bool* p_open)
                     ImGui::Spacing();
                     ImGui::Separator();
                     ImGui::Spacing();
-                    
-                    float btnW = (ImGui::GetContentRegionAvail().x - ImGui::GetStyle().ItemSpacing.x) * 0.5f;
-                    if (ImGui::Button(TR("cancel"), ImVec2(btnW, 40))) {
+
+                    bool doCancel = false, doConfirm = false;
+                    material::DialogConfirmFooter(TR("cancel"), TrId("clear_anyway", "clear_ztx_w").c_str(),
+                                                  true, doCancel, doConfirm);
+                    if (doCancel) {
                         s_confirm_clear_ztx = false;
                     }
-                    ImGui::SameLine();
-                    ImGui::PushStyleColor(ImGuiCol_Button, ImVec4(0.8f, 0.2f, 0.2f, 1.0f));
-                    ImGui::PushStyleColor(ImGuiCol_ButtonHovered, ImVec4(0.9f, 0.3f, 0.3f, 1.0f));
-                    if (ImGui::Button(TrId("clear_anyway", "clear_ztx_w").c_str(), ImVec2(btnW, 40))) {
+                    if (doConfirm) {
                         std::string ztx_file = util::Platform::getDragonXDataDir() + "ztx_history.json";
                         if (util::Platform::deleteFile(ztx_file)) {
                             Notifications::instance().success("Z-transaction history cleared");
@@ -517,7 +512,6 @@ void RenderSettingsWindow(App* app, bool* p_open)
                         }
                         s_confirm_clear_ztx = false;
                     }
-                    ImGui::PopStyleColor(2);
                     material::EndOverlayDialog();
                 }
             }