refactor(media): split the plyr specifics out of the media player composable

[skjnldsv]

Plyr is deprecated (security fixes only), so I'm moving the player to Video.js 10 in #128. This splits usePlyrPlayer first: useMediaPlayer keeps our logic, usePlyrAdapter keeps the Plyr bits, so the swap only replaces the adapter.

No behaviour change, the tests only had their imports updated.

👾 This pull request was assisted by Claude Code, commits carry an Assisted-by trailer.

[codecov]

Codecov Report

❌ Patch coverage is 94.50549% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.39%. Comparing base (f8edb26) to head (038484d).
⚠️ Report is 27 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/composables/usePlyrAdapter.ts	95.65%	3 Missing ⚠️
lib/composables/useMediaPlayer.ts	83.33%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #127      +/-   ##
==========================================
+ Coverage   91.05%   91.39%   +0.33%     
==========================================
  Files          41       42       +1     
  Lines        3421     3556     +135     
  Branches      790      817      +27     
==========================================
+ Hits         3115     3250     +135     
+ Misses        288      287       -1     
- Partials       18       19       +1     

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