fix: update innertube clients and fix HLS/DASH quality switching

- Update innertube client versions to match yt-dlp (android 21.02.35,
  ios 21.02.3, web 2.20260114.08.00, android_vr 1.65.10)
- Remove obsolete clients (android-test-suite, ios_vr)
- Replace tv_embedded with TVHTML5_SIMPLY (cn 75)
- Add new clients: web_embedded, mweb, tv
- Fix HLS freeze on quality switch: use nextLevel instead of
  currentLevel, handle bufferStalledError, stream proxy segments
  instead of buffering in memory
- Populate DASH quality selector with actual sources (no Auto)
- Render quality-select empty in template, let JS populate per mode

youtube/watch_formats.py

@@ -0,0 +1,82 @@
+"""Video format helpers for yt-local."""
+
+import math
+from typing import Any, Dict, Optional
+
+
+def codec_name(vcodec: str) -> str:
+    """Extract codec short name from codec string."""
+    if vcodec.startswith('avc'):
+        return 'h264'
+    elif vcodec.startswith('av01'):
+        return 'av1'
+    elif vcodec.startswith('vp'):
+        return 'vp'
+    else:
+        return 'unknown'
+
+
+def video_quality_string(fmt: Dict[str, Any]) -> str:
+    """Return video quality string (e.g., '1920x1080 30fps')."""
+    if fmt.get('vcodec'):
+        result = f"{fmt.get('width') or '?'}x{fmt.get('height') or '?'}"
+        if fmt.get('fps'):
+            result += f" {fmt['fps']}fps"
+        return result
+    elif fmt.get('acodec'):
+        return 'audio only'
+    return '?'
+
+
+def short_video_quality_string(fmt: Dict[str, Any]) -> str:
+    """Return short video quality string (e.g., '1080p60 AV1')."""
+    result = f"{fmt.get('quality') or '?'}p"
+    if fmt.get('fps'):
+        result += str(fmt['fps'])
+    vcodec = fmt.get('vcodec', '')
+    if vcodec.startswith('av01'):
+        result += ' AV1'
+    elif vcodec.startswith('avc'):
+        result += ' h264'
+    else:
+        result += f" {vcodec}"
+    return result
+
+
+def audio_quality_string(fmt: Dict[str, Any]) -> str:
+    """Return audio quality string (e.g., '128k 44.1kHz')."""
+    if fmt.get('acodec'):
+        if fmt.get('audio_bitrate'):
+            result = f"{fmt['audio_bitrate']}k"
+        else:
+            result = '?k'
+        if fmt.get('audio_sample_rate'):
+            result += f" {'%.3G' % (fmt['audio_sample_rate']/1000)}kHz"
+        return result
+    elif fmt.get('vcodec'):
+        return 'video only'
+    return '?'
+
+
+def format_bytes(bytes_val: Optional[float]) -> str:
+    """Convert bytes to human-readable string (e.g., '1.5 MiB')."""
+    if bytes_val is None:
+        return 'N/A'
+    if type(bytes_val) is str:
+        bytes_val = float(bytes_val)
+    if bytes_val == 0.0:
+        exponent = 0
+    else:
+        exponent = int(math.log(bytes_val, 1024.0))
+    suffix = ['B', 'KiB', 'MiB', 'GiB', 'TiB', 'PiB', 'EiB', 'ZiB', 'YiB'][exponent]
+    converted = float(bytes_val) / float(1024 ** exponent)
+    return '%.2f%s' % (converted, suffix)
+
+
+__all__ = [
+    'codec_name',
+    'video_quality_string',
+    'short_video_quality_string',
+    'audio_quality_string',
+    'format_bytes',
+]