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/Main.qml

@@ -192,6 +192,25 @@ Window {
         z: 20
     }
 
+    // Periodic announcement ("удерживайте кнопку"); config section "banner".
+    InfoBanner {
+        id: infoBanner
+        anchors.left: parent.left
+        anchors.right: parent.right
+        anchors.margins: 12
+        y: settingsContainer.bannerPosition === "top"
+           ? 12 : parent.height - height - 12
+        z: 30
+        suppressed: splash.active || root.secureDialogOpen
+    }
+
+    // Boot splash over everything in the window (dialogs live in the overlay
+    // layer, but none can be open this early).
+    SplashOverlay {
+        id: splash
+        z: 900
+    }
+
     Connections {
         target: settingsContainer
         onChanged: root.hideSensorsIfDisabled()
@@ -304,6 +323,7 @@ Window {
 
     SettingsDialog {
         id: settingsDialog
+        onBannerPreview: infoBanner.preview()
     }
 
     InputPanel {