Add a source picker to search and use the full window width

Search now queries YouTube and SoundCloud together by default and
interleaves the two result lists so neither buries the other; a picker
left of the input narrows it to one source (plus the local library when
configured), and a prefix typed into the query still outranks it.

The panel was capped at 1180px, which left most of a wide screen empty —
it now scales to 1680px and gives the search column the extra room.

A dead link also reported "could not parse yt-dlp's response", which
described our parser rather than the problem; it now shows yt-dlp's own
error line, or says the link did not open.

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

src/core/manager.ts

@@ -1,7 +1,7 @@
 import { EventEmitter } from "node:events";
 import { config } from "../config.js";
 import { logger } from "../logger.js";
-import { NOTHING_FOUND, resolveQuery, searchTracks } from "../sources/index.js";
+import { NOTHING_FOUND, resolveQuery, searchTracks, type SearchSource } from "../sources/index.js";
 import {
   UserFacingError,
   type LoopMode,
@@ -223,8 +223,13 @@ export class MusicManager extends EventEmitter<ManagerEvents> {
     };
   }
 
-  search(query: string, requester: Requester, limit?: number): Promise<Track[]> {
-    return searchTracks(query, requester, limit);
+  search(
+    query: string,
+    requester: Requester,
+    limit?: number,
+    source: SearchSource = "all",
+  ): Promise<Track[]> {
+    return searchTracks(query, requester, limit, source);
   }
 
   private async require(serverId: string, userId: string): Promise<GuildPlayer> {