feat(sui-bundler): add plainCssPackages config to bypass sass-loader

[tomasmax]

Summary

Adds a new plainCssPackages config option to sui-bundler that allows consumer apps to specify npm packages whose .css files should be loaded with only css-loader (and the appropriate style/extract loader), completely bypassing @s-ui/sass-loader and postcss-loader.

Problem

sui-bundler routes all .css and .scss files through the full Sass + PostCSS pipeline — including third-party packages that ship pre-compiled Tailwind CSS v4 output. Dart Sass interprets valid CSS constructs (like transition-property: transform, ...) as Sass spread syntax, causing fatal build errors:

Error: expected ";"
  ╷
  │ transition-property:transform,...;
  │                               ^^^
  ╵

This blocks any consumer app from importing packages that emit modern CSS not compatible with the Sass parser (e.g. @adv-mt/ui which uses Tailwind CSS v4).

Solution

A new config key plainCssPackages under config.sui-bundler in the consumer's package.json:

{
  "config": {
    "sui-bundler": {
      "plainCssPackages": ["@adv-mt/ui", "@adv-mt/theme"]
    }
  }
}

When set, the bundler:

1. Excludes those packages from the main Sass/PostCSS rule via a regex on node_modules/<package>/
2. Adds a separate rule that matches only .css files from those packages, using just css-loader (+ MiniCssExtractPlugin.loader or style-loader depending on the webpack config)

Files changed

File	Change
shared/module-rules-sass.js	Core logic — builds exclude regex, creates separate plain CSS rule, exports array when needed
webpack.config.client.dev.js	Uses shared sassRules (was duplicating inline rules)
webpack.config.dev.js	Adds plainCssPackages support with style-loader (SPA dev mode)
webpack.config.prod.js	Spreads sassRules as array
webpack.config.lib.js	Spreads sassRules as array

Usage

// consumer package.json
{
  "config": {
    "sui-bundler": {
      "plainCssPackages": ["@adv-mt/ui"]
    }
  }
}

Then import '@adv-mt/ui/styles.css' works without Sass compilation errors.

Test plan

• Verified locally: copied broken @adv-mt/ui@2.3.0 CSS into a test app with patched bundler → build passes (no Sass errors)
• Lint passes (npx sui-lint js — 0 errors)
• CI (this PR)

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