refactor: CSS tasks 1-6 — add token aliases, fix all primitive leaks

- Rename 01-asw.css → 01-tokens.css (pure :root, no rules)
- Add semantic aliases: --weight-*, --shadow-*, --focus-ring-width,
  --dropdown-min-width, --space-5a, --weight-light, --border-width-thick
- Extract editorial rules from token file to components/layout
- Replace all Open Props primitives in layers 02-09 with semantic aliases
- Zero primitive leaks remain outside 01-tokens.css

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

src/layers/09-landing.css

@@ -44,7 +44,7 @@
 
 [data-layout="hero"] h1 {
   font-size: clamp(2.6rem, 6vw, 4.5rem);
-  font-weight: var(--font-weight-2);
+  font-weight: var(--weight-light);
   letter-spacing: -0.025em;
   line-height: 1.05;
   margin-bottom: var(--space-4);