Release v0.4.0 - HD Thumbnails, YouTube 2024+ Support, and yt-dlp Integration

Major Features:
- HD video thumbnails (hq720.jpg) with automatic fallback to lower qualities
- HD channel avatars (240x240 instead of 88x88)
- YouTube 2024+ lockupViewModel support for channel playlists
- youtubei/v1/browse API integration for channel playlist tabs
- yt-dlp integration for multi-language audio and subtitles

Bug Fixes:
- Fixed undefined `abort` import in playlist.py
- Fixed undefined functions in proto.py (encode_varint, bytes_to_hex, succinct_encode)
- Fixed missing `traceback` import in proto_debug.py
- Fixed blurry playlist thumbnails using default.jpg instead of HD versions
- Fixed channel playlists page using deprecated pbj=1 format

Improvements:
- Automatic thumbnail fallback system (hq720 → sddefault → hqdefault → mqdefault → default)
- JavaScript thumbnail_fallback() handler for 404 errors
- Better thumbnail quality across all pages (watch, channel, playlist, subscriptions)
- Consistent HD avatar display for all channel items
- Settings system automatically adds new settings without breaking user config

Files Modified:
- youtube/watch.py - HD thumbnails for related videos and playlist items
- youtube/channel.py - HD thumbnails for channel playlists, youtubei API integration
- youtube/playlist.py - HD thumbnails, fixed abort import
- youtube/util.py - HD thumbnail URLs, avatar HD upgrade, prefix_url improvements
- youtube/comments.py - HD video thumbnail
- youtube/subscriptions.py - HD thumbnails, fixed abort import
- youtube/yt_data_extract/common.py - lockupViewModel support, extract_lockup_view_model_info()
- youtube/yt_data_extract/everything_else.py - HD playlist thumbnails
- youtube/proto.py - Fixed undefined function references
- youtube/proto_debug.py - Added traceback import
- youtube/static/js/common.js - thumbnail_fallback() handler
- youtube/templates/*.html - Added onerror handlers for thumbnail fallback
- youtube/version.py - Bump to v0.4.0

Technical Details:
- All thumbnail URLs now use hq720.jpg (1280x720) when available
- Fallback handled client-side via JavaScript onerror handler
- Server-side avatar upgrade via regex in util.prefix_url()
- lockupViewModel parser extracts contentType, metadata, and first_video_id
- Channel playlist tabs now use youtubei/v1/browse instead of deprecated pbj=1
- Settings version system ensures backward compatibility

youtube/templates/watch.html

@@ -85,6 +85,16 @@
                             <option value='{"type": "pair", "index": {{ loop.index0}}}' {{ 'selected' if loop.index0 == pair_idx and using_pair_sources else '' }} >{{ src_pair['quality_string'] }}</option>
                         {% endfor %}
                     </select>
+
+                    {% if audio_tracks and audio_tracks|length > 1 %}
+                    <select id="audio-language-select" autocomplete="off" title="Audio language">
+                        {% for track in audio_tracks %}
+                            <option value="{{ track.get('track_id', track['language']) }}" {{ 'selected' if loop.index0 == 0 else '' }}>
+                                🔊 {{ track['language_name'] }}{% if track.get('is_default') %} (Default){% endif %}
+                            </option>
+                        {% endfor %}
+                    </select>
+                    {% endif %}
                 {% endif %}
             </div>
             <input class="v-checkbox" name="video_info_list" value="{{ video_info }}" form="playlist-edit" type="checkbox">
@@ -246,6 +256,38 @@
      let storyboard_url = {{ storyboard_url | tojson }};
      // @license-end
     </script>
+
+    <!-- Audio language selector handler -->
+    <script>
+     // @license magnet:?xt=urn:btih:0b31508aeb0634b347b8270c7bee4d411b5d4109&dn=agpl-3.0.txt AGPL-v3-or-Later
+     (function() {
+         'use strict';
+         const audioSelect = document.getElementById('audio-language-select');
+         const qualitySelect = document.getElementById('quality-select');
+
+         if (audioSelect && qualitySelect) {
+             audioSelect.addEventListener('change', function() {
+                 const selectedAudio = this.value;
+                 const selectedQuality = qualitySelect.value;
+
+                 // Parse current quality selection
+                 let qualityData;
+                 try {
+                     qualityData = JSON.parse(selectedQuality);
+                 } catch(e) {
+                     return;
+                 }
+
+                 // Reload video with new audio language
+                 const currentUrl = new URL(window.location.href);
+                 currentUrl.searchParams.set('audio_lang', selectedAudio);
+                 window.location.href = currentUrl.toString();
+             });
+         }
+     }());
+     // @license-end
+    </script>
+
     <script src="/youtube.com/static/js/common.js"></script>
     <script src="/youtube.com/static/js/transcript-table.js"></script>
     {% if settings.use_video_player == 2 %}