Suspend rotation while a live wallpaper is on screen

The extension's own log showed rotation kept firing ("Wallpaper
changed to ...") after live wallpaper playback had already started.
Each rotation change writes org.gnome.desktop.background's
picture-uri, which makes GNOME Shell repaint its own background actor
into the same _backgroundGroup our live wallpaper actor lives in,
landing on top of it and hiding the video/GIF entirely.

LiveWallpaperManager now takes an onActiveChanged callback, invoked
only on actual start/stop transitions, which extension.js uses to
suspend/unsuspend RotationManager. This is tracked separately from
user-initiated pause()/resume() so turning live wallpaper off restores
whatever rotation state the user actually had, and next()/previous()
now no-op while suspended so manual/forced-OLED wallpaper changes
can't sneak one in either. The indicator's "Next Wallpaper" item is
greyed out to match.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019RDqbdjsiisSU7CbQke4g8

lib/liveWallpaper.js

@@ -21,9 +21,10 @@ import {loadGstreamerModules, GSTREAMER_INSTALL_HINT} from './gstreamerAvailabil
  * that belongs to gnome-shell itself.
  */
 export class LiveWallpaperManager {
-    constructor(settings, logger) {
+    constructor(settings, logger, {onActiveChanged} = {}) {
         this._settings = settings;
         this._logger = logger;
+        this._onActiveChanged = onActiveChanged ?? (() => {});
 
         this._available = false;
         this._active = false;
@@ -57,6 +58,13 @@ export class LiveWallpaperManager {
         return this._active;
     }
 
+    _setActive(active) {
+        if (this._active === active)
+            return;
+        this._active = active;
+        this._onActiveChanged(active);
+    }
+
     async enable() {
         await this._loadGstreamer();
 
@@ -149,7 +157,7 @@ export class LiveWallpaperManager {
             this._applyMute();
             this._playbin.set_state(Gst.State.PLAYING);
 
-            this._active = true;
+            this._setActive(true);
             this._paused = false;
             this._connectPowerWatches();
             this._logger.debug(`Live wallpaper started: ${path}`);
@@ -336,7 +344,7 @@ export class LiveWallpaperManager {
         this._videoWidth = 0;
         this._videoHeight = 0;
 
-        this._active = false;
+        this._setActive(false);
         this._paused = false;
     }
 }