Refactor Tailwind CSS setup and introduce OKLCH-based design system

- **Tailwind Config:** Clear custom config path and update base color to `zinc`.
- **Design System:** Replace existing CSS with OKLCH color model for improved accessibility and uniformity.
- **Typography & Themes:** Use Geist fonts, define light/dark themes with enhanced semantic variables.
- **Global Styles:** Add consistent border colors, smooth transitions, and reusable variables for Tailwind integration.

frontend/components.json

@@ -4,9 +4,9 @@
   "rsc": true,
   "tsx": true,
   "tailwind": {
-    "config": "tailwind.config.ts",
+    "config": "",
     "css": "src/app/globals.css",
-    "baseColor": "slate",
+    "baseColor": "zinc",
     "cssVariables": true,
     "prefix": ""
   },