Boot splash and periodic announcement banner

Splash: resources/splash/splash.gif built into the binary, played once by
SplashOverlay over a black cover present from the first frame (no UI
flash), then fades into the UI; hides icons loading. GIF, so no
QtMultimedia/gstreamer. Toggle: splash.enabled.

Banner (InfoBanner): metro-style band that fades/slides in with a hold
pictogram; text that does not fit runs as a seamless ticker for two
rounds. Never takes touches; hidden during splash and settings. Config
section banner (enabled, text, intervalSec, showSec, position,
accentColor), editable in the web UI and on-device settings; shown once
after saving.

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

qml/settings/MainPage.qml

@@ -53,6 +53,7 @@ Item {
     signal openLayout()
     signal openBackground()
     signal openFeedback()
+    signal openBanner()
     signal openNetwork()
     signal openUpdate()
     signal changePassword()
@@ -99,6 +100,12 @@ Item {
                 text: "Обводка отклика (ОК / Ошибка)"
                 onClicked: page.openFeedback()
             }
+            SettingsButton {
+                Layout.fillWidth: true
+                text: "Объявление и заставка" +
+                      (settingsContainer.bannerEnabled ? " (вкл.)" : "")
+                onClicked: page.openBanner()
+            }
             SettingsButton {
                 Layout.fillWidth: true
                 text: "Сеть"