fix(api): use MessageMediaType enum for poll checks

Replace string comparisons with the MessageMediaType.POLL enum and add the
necessary import. This ensures poll messages are correctly identified and
skipped during media processing.

post_parser.py

@@ -650,7 +650,7 @@ class PostParser:
 
         content_media = []
         base_url = Config['pyrogram_bridge_url']
-        if message.media and message.media != "MessageMediaType.POLL":
+        if message.media and message.media != MessageMediaType.POLL:
             content_media.append(f'<div class="message-media">')
 
             file_unique_id = self._get_file_unique_id(message)