feat(ui): migrate Validate-address, Address-label & Contacts modals to reference design

Presentation-only reference-design migration of three more modals:
- Validate Address: struct-form overlay (idSuffix validateaddr), 3 StyledButton ->
  TactileButton, drop the description divider, and TR() the hardcoded "Error: %s"
  (reuse the existing error_format key). The validateaddress RPC/worker path is untouched.
- Address label: struct-form overlay (idSuffix addrlabel); drop the footer divider and
  zero its layout-reserve term (separatorH) so the fixed-height icon-picker card math
  stays consistent. Buttons were already TactileButton.
- Contacts add/edit: struct-form overlay (keeps its idSuffix + BeginOverlayDialogFooter);
  StyledButton -> TactileButton across the file (3 modal + 4 contact-list buttons) for a
  consistent Contacts tab. The address-book add/update/notify logic is untouched.

Build + hygiene clean.

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

src/ui/windows/address_label_dialog.h

@@ -61,7 +61,12 @@ public:
 
         constexpr float cardTopViewportRatio = 0.15f;
         constexpr float cardBottomViewportRatio = 0.80f;
-        if (BeginOverlayDialog(TR("set_label"), &s_open, 660.0f, 0.92f, cardBottomViewportRatio)) {
+        OverlayDialogSpec ov;
+        ov.title = TR("set_label"); ov.p_open = &s_open;
+        ov.style = OverlayStyle::BlurFloat;
+        ov.cardWidth = 660.0f; ov.idSuffix = "addrlabel";
+        ov.cardBottomViewportRatio = cardBottomViewportRatio;
+        if (BeginOverlayDialog(ov)) {
             float dp = Layout::dpiScale();
 
             // Address preview
@@ -108,7 +113,7 @@ public:
             const bool showClearIcon = (s_selectedIcon >= 0);
             const float clearRowH = showClearIcon ? ImGui::GetTextLineHeight() : 0.0f;
             const float buttonRowH = ImGui::GetFrameHeight();
-            const float separatorH = 1.0f;
+            const float separatorH = 0.0f;   // footer divider removed (reference design)
             const float preButtonReserve =
                 (showClearIcon ? (style.ItemSpacing.y + clearRowH) : 0.0f) +
                 style.ItemSpacing.y * 3.0f + separatorH;
@@ -196,7 +201,6 @@ public:
 
             ImGui::Spacing();
             ImGui::Spacing();
-            ImGui::Separator();
             ImGui::Spacing();
 
             if (ImGui::GetCursorPosY() < buttonY) {