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_book_dialog.cpp

@@ -258,7 +258,7 @@ void AddressBookDialog::render(App* app)
                     }
                     ImGui::TextDisabled("%s", addr_display.c_str());
                     if (ImGui::IsItemHovered()) {
-                        ImGui::SetTooltip("%s", entry.address.c_str());
+                        material::Tooltip("%s", entry.address.c_str());
                     }
                     
                     ImGui::TableNextColumn();