fix: Stop repeating the license header in every compiled stylesheet

[TrevorBurnham]

Description

Fixes #4905.

Sass copies loud comments into the compiled CSS, so each partial's license header was emitted once per entry point that @uses it. Every published stylesheet carried a median of 34 copies, and 580 KB of the 2305 KB of CSS was the same four lines repeated.

The 91 partials under src/ now declare the header with Sass line comments, which the compiler strips. The styles.scss entry points keep the block comment, so every output file still carries one. .stylelintrc enforces the right form for each using the commentType option added in cloudscape-design/build-tools#75.

	before	after
CSS, raw	2305 KB	1745 KB (-24.3%)
CSS, gzipped	303 KB	298 KB (-1.8%)
license header bytes	580 KB (25.2%)	32 KB (1.8%)
headers, total	5400	297
headers per stylesheet, median	34	1
headers per stylesheet, max	51	5
stylesheets with more than one	152	48

The gzipped win is small because gzip already deduped the identical blocks. The win is in unminified bytes, which is what dev servers serve and what the internal package ships. Minified production bundles are unaffected either way, since minifiers strip the comments already.

Two things reviewers should know:

1. Every generated scoped class name changes. The name is awsui_{name}_{fileHash}_{contentHash}_{lineNumber}, and removing comments moves both the content hash and the line numbers. No snapshot needs updating, though: the test-utils selectors snapshot truncates to the path-derived hash, and since #4936, keyframe names derive from stable per-keyframe hashes rather than from a hash of src/internal/styles/global.scss, so the design tokens and themes snapshots no longer move with this change either. The compiled CSS is otherwise identical, verified as described below.

2. This does not remove every duplicate. 48 stylesheets still carry more than one header, up to 5. That remainder is a Dart Sass behaviour, not something this repo controls: an entry point's leading comments are re-emitted once per module when the entry point and its partials share a dependency. Minimal repro on Sass 1.89.2, no Cloudscape code involved:

// _shared.scss
.shared { color: gray; }
@mixin m { color: gray; }

// _a.scss     -> @use "shared";  .a { color: red; }
// _b.scss     -> @use "shared";  .b { color: blue; }

// entry.scss
/* ENTRY HEADER */
@use "shared";
@use "a";
@use "b";

ENTRY HEADER is emitted three times. This is the shape of every Cloudscape component that has sub-partials, which is why popover still ends up with several headers rather than one. It accounts for roughly 6 KB and is worth a follow-up upstream; it does not block this change.

The other source named in #4905, @cloudscape-design/component-toolkit, is already resolved: cloudscape-design/component-toolkit#248 converted its two SCSS files and shipped in 1.0.0-beta.182, which this branch builds against. That is why the median here reaches 1 rather than 2.

How has this been tested?

A normalised comparison of all 229 compiled stylesheets against a build of main from the same node_modules. After neutralising license blocks and the contentHash/lineNumber segments of scoped names, all 229 stylesheets are byte-identical. No file was added, removed, or left empty.

Review checklist

The following items are to be evaluated by the author(s) and the reviewer(s).

Correctness

• Changes include appropriate documentation updates.
• Changes are backward-compatible if not indicated, see CONTRIBUTING.md.
• Changes do not include unsupported browser features, see CONTRIBUTING.md.
• Changes were manually tested for accessibility, see accessibility guidelines.

Testing

• Changes are covered with new/existing unit tests?
• Changes are covered with new/existing integration tests?

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.75%. Comparing base (a420fd6) to head (582c306).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4906      +/-   ##
==========================================
- Coverage   97.66%   93.75%   -3.92%     
==========================================
  Files         959      958       -1     
  Lines       31342    27138    -4204     
  Branches    11577     9345    -2232     
==========================================
- Hits        30610    25443    -5167     
- Misses        725      790      +65     
- Partials        7      905     +898     

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