fix: add typescript as explicit devDependency

pnpm run tsc failed with "tsc not found" because typescript was only
available as a transitive dependency from @kinvolk/headlamp-plugin.
Adding it explicitly as a direct devDependency ensures tsc is always
accessible regardless of pnpm hoisting behavior.

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

package.json

@@ -49,6 +49,7 @@
     "react-dom": "^18.3.1",
     "react-router-dom": "^5.3.0",
     "tar": "^7.5.11",
+    "typescript": "~5.6.2",
     "undici": "^7.24.3",
     "vitest": "^3.0.5"
   }