feat: add Spanish README and improve channel/playlist handling

* Add complete Spanish translation (README.es.md)
* Restructure English README for clarity and conciseness
* Filter out YouTube Shorts from channel video listings (sort=4)
* Add fallback for video count using playlist metadata when API returns zero
* Add get_playlist_metadata() to fetch metadata without full video list
* Add is_short() utility to detect YouTube Shorts by duration, badges, and type
* Export is_short from yt_data_extract for use across modules

youtube/playlist.py

@@ -28,6 +28,32 @@ def playlist_ctoken(playlist_id, offset, include_shorts=True):
     return base64.urlsafe_b64encode(pointless_nest).decode('ascii')
 
 
+def get_playlist_metadata(playlist_id, report_text="Retrieved playlist metadata"):
+    """Get playlist metadata (video_count, title, etc.) without fetching videos."""
+    key = 'AIzaSyAO_FJ2SlqU8Q4STEHLGCilw_Y9_11qcW8'
+    url = f'https://www.youtube.com/youtubei/v1/browse?key={key}'
+
+    data = {
+        'context': {
+            'client': {
+                'hl': 'en',
+                'gl': 'US',
+                'clientName': 'WEB',
+                'clientVersion': '2.20240327.00.00',
+            },
+        },
+        'browseId': 'VL' + playlist_id,
+    }
+
+    content_type_header = (('Content-Type', 'application/json'),)
+    content = util.fetch_url(
+        url, util.desktop_xhr_headers + content_type_header,
+        data=json.dumps(data),
+        report_text=report_text, debug_name='playlist_metadata'
+    )
+    return json.loads(content.decode('utf-8'))
+
+
 def playlist_first_page(playlist_id, report_text="Retrieved playlist",
                         use_mobile=False):
     # Use innertube API (pbj=1 no longer works for many playlists)