docs: add CSS variable rule to CLAUDE.md

Always use design system CSS variables for colors, never hardcode hex.
Applies to CSS modules, inline styles, and SVG fill/stroke attributes.

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

CLAUDE.md

@@ -57,6 +57,10 @@ java -jar cameleer3-server-app/target/cameleer3-server-app-1.0-SNAPSHOT.jar
 - K8s probes: server uses `/api/v1/health`, PostgreSQL uses `pg_isready`, OpenSearch uses `/_cluster/health`
 - Docker build uses buildx registry cache + `--provenance=false` for Gitea compatibility
 
+## UI Styling
+
+- Always use `@cameleer/design-system` CSS variables for colors (`var(--amber)`, `var(--error)`, `var(--success)`, etc.) — never hardcode hex values. This applies to CSS modules, inline styles, and SVG `fill`/`stroke` attributes. SVG presentation attributes resolve `var()` correctly.
+
 ## Disabled Skills
 
 - Do NOT use any `gsd:*` skills in this project. This includes all `/gsd:` prefixed commands.