fix(types): make ParsedPlaylistItem.url optional to match runtime

The parser fork's d.ts now truthfully declares url?: string (a trailing
#EXTINF without a stream URL yields url === undefined at runtime, and
always has). The local ParsedPlaylistItem mirrored the old type lie and
made the production typecheck reject the parser's Playlist type.
createChannel and createPlaylistObject already tolerate the absent url.

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

libs/shared/interfaces/src/lib/parsed-playlist.interface.ts

@@ -22,7 +22,8 @@ export interface ParsedPlaylistItem {
         referrer: string;
         'user-agent': string;
     };
-    url: string;
+    /** absent when an #EXTINF entry has no stream URL (e.g. truncated file) */
+    url?: string;
     raw: string;
     catchup?: {
         type?: string;