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>

wrangler-example.toml

@@ -13,6 +13,11 @@ kv_namespaces = [
 #   { binding = "ATTACHMENT_BUCKET", bucket_name = "REPLACE_WITH_YOUR_BUCKET_NAME", preview_bucket_name = "REPLACE_WITH_YOUR_PREVIEW_BUCKET_NAME" }
 # ]
 
+# Import CSS files as text strings (inlined in HTML <style> tags)
+[[rules]]
+type = "Text"
+globs = ["**/*.css"]
+
 # Workers Observability (keeps config in sync with dashboard toggle)
 [observability.logs]
 enabled = true