refactor(ui): app-wide compact, translucent tooltips

Add material::Tooltip / BeginTooltip / EndTooltip wrappers (tooltip_style.h)
that scope a small window padding (8x4, dpi-scaled) and ~85% opacity to
tooltips only, then route the tooltip call sites through them. Menus and combo
dropdowns are untouched (they keep the global opaque PopupBg).

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

src/ui/windows/address_label_dialog.h

@@ -172,7 +172,7 @@ public:
                 ImGui::PushID(i);
                 ImGui::InvisibleButton("##icon", ImVec2(cellSz, cellSz));
                 if (ImGui::IsItemClicked()) s_selectedIcon = i;
-                if (hov) ImGui::SetTooltip("%s", iconName);
+                if (hov) material::Tooltip("%s", iconName);
                 ImGui::PopID();
 
                 col = (col + 1) % cols;