feat(design-system): add Tailwind 4 @theme tokens, fonts, and completeness tests

- Load Fraunces, DM Sans, DM Mono via Google Fonts preconnect in app.html
- Define all design tokens in @theme block: neutrals, green/yellow/blue/
  purple/orange scales, spacing (--space-1..20), radii, shadows, button base
- Note --green-dark as button background (--green fails WCAG AA with white)
- Add @types/node for Node fs/path usage in design-system tests

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

frontend/tsconfig.json

@@ -0,0 +1,21 @@
+{
+	"extends": "./.svelte-kit/tsconfig.json",
+	"compilerOptions": {
+		"rewriteRelativeImportExtensions": true,
+		"allowJs": true,
+		"checkJs": true,
+		"esModuleInterop": true,
+		"forceConsistentCasingInFileNames": true,
+		"resolveJsonModule": true,
+		"skipLibCheck": true,
+		"sourceMap": true,
+		"strict": true,
+		"moduleResolution": "bundler",
+		"types": ["@types/node"]
+	}
+	// Path aliases are handled by https://svelte.dev/docs/kit/configuration#alias
+	// except $lib which is handled by https://svelte.dev/docs/kit/configuration#files
+	//
+	// To make changes to top-level options such as include and exclude, we recommend extending
+	// the generated config; see https://svelte.dev/docs/kit/configuration#typescript
+}