feat(material): extract DialogActionFooter + GlassSectionScope helpers

Phase 0b of the settings-modal redesign — pull the reference dialog's two
repeated patterns into shared helpers so the upcoming migrations are mechanical
and identical:

- material::DialogActionFooter(primary, enabled, close, &outPrimary, &outClose)
  — the centered fixed-width primary+Close TactileButton pair with no divider.
- material::GlassSectionScope — an RAII auto-sized glass sub-section using a LOCAL
  ImDrawListSplitter (combo-safe, unlike GlassCardScope's shared ChannelsSplit) with
  the reference's 12/10 padding and 8dp rounding; interiorWidth() for full-width kids.

Dogfooded by refactoring renderImportKeyDialog's footer and scan-height panel onto
them — same padding/spec/centering, so the render is unchanged.

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

src/ui/material/draw_helpers.h

@@ -1706,6 +1706,70 @@ inline void DialogConfirmFooter(const char* cancelId, const char* confirmLabel,
     }
 }
 
+// Reference dialog footer: a centered primary + Close (or Cancel) TactileButton pair, fixed width,
+// NO divider above (the reference dropped the separator). Sets outPrimary/outClose when the respective
+// button is clicked — the caller runs the bodies (so the primary's action can be arbitrary). The
+// primary is BeginDisabled'd when !primaryEnabled. btnW<=0 → 130·dp default.
+inline void DialogActionFooter(const char* primaryLabel, bool primaryEnabled,
+                               const char* closeLabel, bool& outPrimary, bool& outClose,
+                               float btnW = 0.0f)
+{
+    const float dp = Layout::dpiScale();
+    if (btnW <= 0.0f) btnW = 130.0f * dp;
+    const float total = btnW * 2.0f + ImGui::GetStyle().ItemSpacing.x;
+    const float off = (ImGui::GetContentRegionAvail().x - total) * 0.5f;
+    if (off > 0.0f) ImGui::SetCursorPosX(ImGui::GetCursorPosX() + off);
+    ImGui::BeginDisabled(!primaryEnabled);
+    if (TactileButton(primaryLabel, ImVec2(btnW, 0))) outPrimary = true;
+    ImGui::EndDisabled();
+    ImGui::SameLine();
+    if (TactileButton(closeLabel, ImVec2(btnW, 0))) outClose = true;
+}
+
+// RAII glass sub-section for grouping an optional/advanced block inside a dialog (the reference's
+// scan-height panel). Auto-sizes to its content and paints a subtle glass panel behind it. Uses a
+// LOCAL ImDrawListSplitter — safe with BeginCombo popups, unlike the shared ChannelsSplit that
+// GlassCardScope uses. padX/padY are the interior insets (in logical px, dp-scaled here). Render the
+// section body between construction and destruction; use interiorWidth() for full-width children.
+struct GlassSectionScope {
+    ImDrawListSplitter splitter;
+    ImDrawList* dl;
+    ImVec2 cardMin;
+    float panelW, padX, padY;
+    GlassPanelSpec spec;
+
+    explicit GlassSectionScope(float padXLogical = 12.0f, float padYLogical = 10.0f)
+    {
+        const float dp = Layout::dpiScale();
+        padX = padXLogical * dp;
+        padY = padYLogical * dp;
+        spec.rounding    = 8.0f * dp;
+        spec.fillAlpha   = 20;
+        spec.borderAlpha = 30;
+        dl = ImGui::GetWindowDrawList();
+        panelW  = ImGui::GetContentRegionAvail().x;
+        cardMin = ImGui::GetCursorScreenPos();
+        splitter.Split(dl, 2);
+        splitter.SetCurrentChannel(dl, 1);   // content above the panel background
+        ImGui::Dummy(ImVec2(0, padY));
+        ImGui::Indent(padX);
+    }
+    ~GlassSectionScope()
+    {
+        ImGui::Unindent(padX);
+        ImGui::Dummy(ImVec2(0, padY));
+        const ImVec2 cardMax(cardMin.x + panelW, ImGui::GetCursorScreenPos().y);
+        splitter.SetCurrentChannel(dl, 0);
+        DrawGlassPanel(dl, cardMin, cardMax, spec);
+        splitter.Merge(dl);
+    }
+    // Interior content width (panel width minus both side insets) for full-width children.
+    float interiorWidth() const { return panelW - 2.0f * padX; }
+
+    GlassSectionScope(const GlassSectionScope&) = delete;
+    GlassSectionScope& operator=(const GlassSectionScope&) = delete;
+};
+
 } // namespace material
 } // namespace ui
 } // namespace dragonx