Add only the track when a link carries both a video and a list

A link copied from an open mix (watch?v=…&list=RD…) expanded into the
whole radio station — 500 entries from one paste. Any URL with a `v=`
parameter now resolves to that single track, and only a /playlist?list=…
URL expands. The rule is deliberately blunt rather than keyed on
start_radio, so pasting a link behaves the same way every time.

Playlist expansion is also capped separately from the queue limit
(MAX_PLAYLIST_TRACKS, 100 by default) and the chat says when a playlist
hit that ceiling.

Verified against the real yt-dlp: both mix links resolve to one track, a
plain video link to one, and a playlist URL to its 13 entries.

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

src/bot/commands.ts

@@ -53,8 +53,10 @@ async function playCommand(ctx: CommandContext, mode: "append" | "next" | "now")
   });
 
   if (outcome.playlist) {
+    const capped = outcome.tracks.length >= config.MAX_PLAYLIST_TRACKS;
     await ctx.reply(
-      `📥 Добавлено **${outcome.tracks.length}** треков из плейлиста [${outcome.playlist.title}](${outcome.playlist.url}).`,
+      `📥 Добавлено **${outcome.tracks.length}** треков из плейлиста [${outcome.playlist.title}](${outcome.playlist.url})` +
+        (capped ? ` — это предел на один плейлист (MAX_PLAYLIST_TRACKS).` : "."),
     );
     return;
   }