build: add Wrangler text rule for CSS imports

Add [[rules]] type = "Text" globs = ["**/*.css"] to wrangler-example.toml
so Wrangler bundles .css files as raw text strings importable in TypeScript.
Add src/types/css.d.ts to provide the module declaration for `import css from "*.css"`.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/types/css.d.ts

@@ -0,0 +1,4 @@
+declare module "*.css" {
+  const content: string;
+  export default content;
+}