Make video a per-server toggle instead of an env-wide setting

VIDEO_ENABLED is now permission rather than behaviour: it decides whether
the feature exists at all, while turning it on for a server is a toggle in
the panel or !video in chat, off by default. Video costs real CPU for
every playing channel, so that should be a deliberate choice rather than
something a config flag switches on everywhere.

With the env flag off the panel renders no toggle at all and !video says
so, and the switch applies from the next track — swapping tracks mid-play
would cut the current one.

The loop button no longer reads "выкл" either: it sat next to the video
button showing the same word, so the two states were indistinguishable.
Both now name what they do and rely on highlighting for state.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/core/player.ts

@@ -66,7 +66,9 @@ export class GuildPlayer extends EventEmitter<GuildPlayerEvents> {
   current: Track | null = null;
   volume = config.DEFAULT_VOLUME;
   loop: LoopMode = "off";
-  shuffleUsed = false;
+  shuffleUsed = false;
+  /** Per-server switch for publishing the clip; the env flag gates it too. */
+  videoEnabled = false;
 
   private status: PlayerStatus = "idle";
   private readonly revoice: RevoiceLike;
@@ -113,7 +115,8 @@ export class GuildPlayer extends EventEmitter<GuildPlayerEvents> {
       history: this.history.slice(0, 10),
       volume: this.volume,
       loop: this.loop,
-      shuffleUsed: this.shuffleUsed,
+      shuffleUsed: this.shuffleUsed,
+      videoEnabled: this.videoEnabled,
       updatedAt: Date.now(),
     };
   }
@@ -307,7 +310,7 @@ export class GuildPlayer extends EventEmitter<GuildPlayerEvents> {
     this.publish();
 
     try {
-      const input = await openPlayback(track, seekSeconds);
+      const input = await openPlayback(track, seekSeconds, { video: this.videoEnabled });
       this.currentInput = input;
       this.expectingStop = false;
       await media.playStream(input.input, input.inputOptions);
@@ -464,6 +467,12 @@ export class GuildPlayer extends EventEmitter<GuildPlayerEvents> {
     this.publish();
   }
 
+  /** Takes effect on the next track: switching mid-stream would cut playback. */
+  setVideo(enabled: boolean): void {
+    this.videoEnabled = enabled;
+    this.publish();
+  }
+
   setLoop(mode: LoopMode): void {
     this.loop = mode;
     this.publish();