refactor: restructure repo into src/ site/ dist/ vendor/ packs/

Separate framework source from website:
- src/layers/ + src/main.css: CSS framework source (was assets/css/)
- site/: Hugo website (content/, layouts/, hugo.toml)
- dist/: built output (asw.css, asw.min.css)
- vendor/open-props/: vendored dependency with version tracking
- Hugo module mounts: dist/ → static, site runs from site/

Build: hugo --source site/ passes (105 pages).
npm run build produces dist/asw.css.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

vendor/README.md

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+# vendor/
+
+Third-party CSS files vendored directly into the repo so the build has no runtime npm dependency.
+
+## Contents
+
+| Directory | Package | Version | Files vendored |
+|-----------|---------|---------|----------------|
+| `open-props/` | [open-props](https://open-props.style/) | 1.7.23 | `open-props.min.css`, `media.min.css` |
+
+## How to update
+
+1. Bump the version in `package.json` and run `npm install`.
+2. Copy the new files:
+   ```bash
+   cp node_modules/open-props/open-props.min.css vendor/open-props/open-props.min.css
+   cp node_modules/open-props/media.min.css      vendor/open-props/media.min.css
+   ```
+3. Update `vendor/open-props/VERSION` with the new version and today's date.
+4. Commit all three changed files together.

vendor/open-props/VERSION

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+open-props@1.7.23 — vendored 2026-04-11

vendor/open-props/media.min.css

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+@custom-media --motionOK      (prefers-reduced-motion: no-preference);@custom-media --motionNotOK   (prefers-reduced-motion: reduce);@custom-media --opacityOK     (prefers-reduced-transparency: no-preference);@custom-media --opacityNotOK  (prefers-reduced-transparency: reduce);@custom-media --useDataOK     (prefers-reduced-data: no-preference);@custom-media --useDataNotOK  (prefers-reduced-data: reduce);@custom-media --OSdark        (prefers-color-scheme: dark);@custom-media --OSlight       (prefers-color-scheme: light);@custom-media --highContrast  (prefers-contrast: more);@custom-media --lowContrast   (prefers-contrast: less);@custom-media --invertedColors  (inverted-colors: inverted);@custom-media --forcedColors  (forced-colors: active);@custom-media --portrait      (orientation: portrait);@custom-media --landscape     (orientation: landscape);@custom-media --HDcolor       (dynamic-range: high) or (color-gamut: p3);@custom-media --touch         (hover: none) and (pointer: coarse);@custom-media --stylus        (hover: none) and (pointer: fine);@custom-media --pointer       (hover) and (pointer: coarse);@custom-media --mouse         (hover) and (pointer: fine);@custom-media --xxs-only       (min-width: 0px) and      (max-width: 239.98px);@custom-media --xxs-n-above (min-width: 240px);@custom-media --xxs-n-below (max-width: 239.98px);@custom-media --xxs-phone     (--xxs-only) and (--portrait);@custom-media --xs-only        (min-width: 240px) and       (max-width: 359.98px);@custom-media --xs-n-above (min-width: 360px);@custom-media --xs-n-below (max-width: 359.98px);@custom-media --xs-phone      (--xs-only) and (--portrait);@custom-media --sm-only        (min-width: 360px) and       (max-width: 479.98px);@custom-media --sm-n-above (min-width: 480px);@custom-media --sm-n-below (max-width: 479.98px);@custom-media --sm-phone      (--sm-only) and (--portrait);@custom-media --md-only        (min-width: 480px) and       (max-width: 767.98px);@custom-media --md-n-above (min-width: 768px);@custom-media --md-n-below (max-width: 767.98px);@custom-media --md-phone      (--md-only) and (--portrait);@custom-media --lg-only        (min-width: 768px) and       (max-width: 1023.98px);@custom-media --lg-n-above (min-width: 1024px);@custom-media --lg-n-below (max-width: 1023.98px);@custom-media --lg-phone      (--lg-only) and (--portrait);@custom-media --xl-only        (min-width: 1024px) and       (max-width: 1439.98px);@custom-media --xl-n-above (min-width: 1440px);@custom-media --xl-n-below (max-width: 1439.98px);@custom-media --xxl-only       (min-width: 1440px) and      (max-width: 1919.98px);@custom-media --xxl-n-above (min-width: 1920px);@custom-media --xxl-n-below (max-width: 1919.98px);