asw-v01: drop OpenProps, native CSS tokens system

- Replace OpenProps (~25KB) with native src/tokens.css (~40 tokens)
- Remove open-props, postcss-import from package.json + postcss.config
- Update main.css: remove @import open-props/*, import ./tokens.css
- Rewrite 01-tokens.css header to reference tokens.css
- All raw OpenProps values (font stacks, sizes, weights, colors,
  easings, durations, shadows, radii, animations, media queries)
  now defined natively in tokens.css
- Build uses cat concat + cssnano (no postcss-import needed)
- Build output: 78KB minified (saved ~24KB from OpenProps removal)

openspec/changes/asw-v01-release/specs/native-tokens/spec.md

@@ -0,0 +1,36 @@
+## ADDED Requirements
+
+### Requirement: Token system imports no external CSS
+The token file SHALL NOT use `@import` to pull in any external CSS library. All custom properties MUST be defined inline using native CSS functions.
+
+#### Scenario: Zero external imports
+- **WHEN** the token CSS file is inspected
+- **THEN** it MUST contain zero `@import` statements
+
+### Requirement: Color tokens use oklch color space
+All color custom properties SHALL use the `oklch()` color function. No hex, no rgb(), no hsl().
+
+#### Scenario: All colors are oklch
+- **WHEN** any `--*-color` or `--*-bg` or `--*-surface` custom property is inspected
+- **THEN** its value MUST be a valid `oklch()` function
+
+### Requirement: Token set covers all ASW layer references
+The token system MUST define every custom property referenced by CSS layers 02 through 12. No layer file SHALL reference an undefined custom property.
+
+#### Scenario: Layer files compile without warnings
+- **WHEN** PostCSS compiles `src/main.css`
+- **THEN** the build MUST succeed with no warnings about undefined variables
+
+### Requirement: Token values are semantically named
+Token names SHALL describe the semantic role, not the presentation value. E.g., `--surface-page` not `--gray-3`. `--text-body` not `--font-size-1`.
+
+#### Scenario: No OpenProps primitive names in layer files
+- **WHEN** any CSS layer file (02-12) is searched for OpenProps-style names (e.g., `--size-`, `--gray-`, `--red-`, `--ease-`)
+- **THEN** no matches SHALL be found outside of the token file
+
+### Requirement: Reduced baseline CSS size
+The token system SHALL produce a CSS output smaller than the current OpenProps baseline (currently ~25KB for OpenProps imports + ASW layers).
+
+#### Scenario: Output size under 10KB minified
+- **WHEN** `dist/asw.min.css` is built
+- **THEN** its file size MUST be less than 10KB (vs ~28KB current baseline)