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/SettingsDialog.qml

@@ -12,6 +12,9 @@ Dialog {
     anchors.centerIn: parent
     standardButtons: Dialog.Close
 
+    // BannerPage "Показать сейчас": the dialog closes, Main shows the banner.
+    signal bannerPreview()
+
     readonly property color panelBg: "#161628"
     readonly property color panelFg: "#ffffff"
     readonly property color panelMuted: "#cccccc"
@@ -49,6 +52,7 @@ Dialog {
             onOpenLayout: stack.push(layoutPageComp)
             onOpenBackground: stack.push(backgroundPageComp)
             onOpenFeedback: stack.push(feedbackPageComp)
+            onOpenBanner: stack.push(bannerPageComp)
             onOpenNetwork: stack.push(networkPageComp)
             onOpenUpdate: stack.push(updatePageComp)
             onChangePassword: changePwdDialog.open()
@@ -68,6 +72,15 @@ Dialog {
     Component { id: feedbackPageComp;   FeedbackPage {} }
     Component { id: networkPageComp;    NetworkInfoPage {} }
     Component { id: updatePageComp;     UpdatePage {} }
+    Component {
+        id: bannerPageComp
+        BannerPage {
+            onPreviewRequested: {
+                dlg.close()
+                dlg.bannerPreview()
+            }
+        }
+    }
 
     ButtonEditorDialog { id: editorDialog }