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/package-lock.json

@@ -19,6 +19,7 @@
 				"@tailwindcss/vite": "^4.2.2",
 				"@testing-library/jest-dom": "^6.9.1",
 				"@testing-library/svelte": "^5.3.1",
+				"@types/node": "^25.5.0",
 				"@vitest/ui": "^4.1.2",
 				"jsdom": "^29.0.1",
 				"openapi-typescript": "^7.13.0",
@@ -1847,6 +1848,16 @@
 			"dev": true,
 			"license": "MIT"
 		},
+		"node_modules/@types/node": {
+			"version": "25.5.0",
+			"resolved": "https://registry.npmjs.org/@types/node/-/node-25.5.0.tgz",
+			"integrity": "sha512-jp2P3tQMSxWugkCUKLRPVUpGaL5MVFwF8RDuSRztfwgN1wmqJeMSbKlnEtQqU8UrhTmzEmZdu2I6v2dpp7XIxw==",
+			"dev": true,
+			"license": "MIT",
+			"dependencies": {
+				"undici-types": "~7.18.0"
+			}
+		},
 		"node_modules/@types/resolve": {
 			"version": "1.20.2",
 			"resolved": "https://registry.npmjs.org/@types/resolve/-/resolve-1.20.2.tgz",
@@ -3737,6 +3748,13 @@
 				"node": ">=20.18.1"
 			}
 		},
+		"node_modules/undici-types": {
+			"version": "7.18.2",
+			"resolved": "https://registry.npmjs.org/undici-types/-/undici-types-7.18.2.tgz",
+			"integrity": "sha512-AsuCzffGHJybSaRrmr5eHr81mwJU3kjw6M+uprWvCXiNeN9SOGwQ3Jn8jb8m3Z6izVgknn1R0FTCEAP2QrLY/w==",
+			"dev": true,
+			"license": "MIT"
+		},
 		"node_modules/uri-js-replace": {
 			"version": "1.0.1",
 			"resolved": "https://registry.npmjs.org/uri-js-replace/-/uri-js-replace-1.0.1.tgz",