fix(ci): add tailwindcss as direct dependency

PostCSS plugin needs tailwindcss package available in node_modules
at build time. Adding it as a direct dependency ensures consistent
resolution.

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

bun.lock

@@ -56,6 +56,7 @@
         "react-router-dom": "^7.15.1",
         "recharts": "3.8.1",
         "tailwind-merge": "^3.6.0",
+        "tailwindcss": "^4.3.1",
         "web-vitals": "5.3.0",
         "zustand": "^5.0.13",
       },