Improve video thumbnails

[daun]

• Increase priority of Mux video thumbnails so they win out over existing FFMPEG thumbnails
• Load thumbnails as webp files for decreased file size
• Scale thumbnails by longest side

[codecov]

Codecov Report

❌ Patch coverage is 80.00000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 59.43%. Comparing base (451c9a3) to head (be02791).
⚠️ Report is 14 commits behind head on main.

Files with missing lines	Patch %	Lines
src/Thumbnails/ThumbnailService.php	80.00%	3 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main      #72      +/-   ##
============================================
- Coverage     59.48%   59.43%   -0.06%     
- Complexity      524      527       +3     
============================================
  Files            53       53              
  Lines          1755     1760       +5     
============================================
+ Hits           1044     1046       +2     
- Misses          711      714       +3     

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