Use native @tailwindcss/webpack loader in preset-tailwindcss-4

[titouanmathis]

Replace @tailwindcss/postcss with the native @tailwindcss/webpack loader introduced in Tailwind CSS v4.2.0. The loader replaces postcss-loader entirely in CSS rules and handles candidate scanning and incremental rebuilds natively. Optimization is disabled (optimize: false) to keep using the existing CssMinimizerPlugin.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (40c0995) to head (cce81a6).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff             @@
##              master      #207   +/-   ##
===========================================
  Coverage     100.00%   100.00%           
===========================================
  Files              6         1    -5     
  Lines            280       191   -89     
===========================================
- Hits             280       191   -89     

Flag	Coverage Δ
unittests	100.00% <ø> (ø)

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