fix: add typescript as direct devDependency (fixes tsc not found)

PR #8 revealed that typescript is also missing as a direct dependency.
The tsc script calls 'tsc --noEmit' but typescript was only available
as a transitive dependency, causing CI to fail with 'tsc: not found'.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

package.json

@@ -34,6 +34,7 @@
     "react": "^18.3.1",
     "react-dom": "^18.3.1",
     "react-router-dom": "^5.3.0",
+    "typescript": "^5.6.2",
     "vitest": "^3.0.5"
   }
 }