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 35 copies, and 598 KB of the 2326 KB of CSS was the same four lines repeated.

The 89 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.

Published CSS drops 2326 KB → 1770 KB (-23.9%). Gzipped it is 306 KB → 300 KB, because gzip already deduped the identical blocks; the win is in unminified bytes, which is what dev servers serve. 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. The test-utils selectors snapshot passes unchanged because it truncates to the path-derived hash. The design tokens snapshot is updated in this PR because tokenStylesSuffix hashes src/internal/styles/global.scss, whose header changed. The compiled CSS is otherwise identical: I diffed all 229 stylesheets before and after, normalising license blocks and generated hashes, and the payload matches everywhere.

2. This does not remove every duplicate. The median goes from 35 to 2, not to 1. The remainder comes from two sources outside this change:

• @cloudscape-design/component-toolkit ships focus-visible/index.scss and style-api/index.scss with block headers. Converting those locally saves a further 17 KB and takes the median to 1.
• Dart Sass re-emits an entry point's leading comments 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. Drop the @use "shared" from the entry, or from _a/_b, and it is emitted once. This is the shape of every Cloudscape component that has sub-partials, which is why popover still ends up with 5 headers rather than 1.

Both are worth follow-ups; neither blocks this change.

How has this been tested?

• npm run lint:stylelint passes with build-tools#75 applied. It fails with 89 Missing license header errors against the currently published build-tools, so this PR is blocked on feat: Add commentType option to the license-headers stylelint rule build-tools#75 merging. That is why it is a draft.
• npm run quick-build, then a byte-level comparison of all 229 compiled stylesheets before and after, as described above.
• npx jest src/popover src/table src/test-utils src/internal/styles — 736 tests pass.
• src/__tests__/snapshot-tests/test-utils-selectors.test.tsx passes with no snapshot change, confirming the public test-utils selectors are unaffected.
• design-tokens.test.ts snapshot updated; the diff is only the tokenStylesSuffix hash.
• documenter.test.ts fails locally on main too, because it needs lib/components-definitions from the full build rather than quick-build. Unrelated.

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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