Settings: Explain the speed hacks on their page instead of in the link

The link is now just "Speed hacks", with a hint under it saying they can
cause rendering errors, and the page starts with a longer explanation.
Adds SettingsPage::Description() for text between the groups.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

UI/SettingsPagesDialogScreen.cpp

@@ -425,6 +425,8 @@ bool SettingsPagesDialogScreen::SearchPage(UI::ViewGroup *parent, int settingsTa
 				show[lastSetting] = true;
 			}
 			break;
+		case SettingType::Description:
+			break;
 		default:
 			lastSetting = i;
 			show[i] = matches || sectionMatches;