Swap plugin-react-swc for plugin-react-oxc

Unifies the transform pipeline on Oxc now that Rolldown does the
bundling. Dev server boot 353ms -> 188ms; build parity (2.03s).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/package.json

@@ -45,7 +45,7 @@
     "@types/node": "^20",
     "@types/react": "^19",
     "@types/react-dom": "^19",
-    "@vitejs/plugin-react-swc": "^3.9.0",
+    "@vitejs/plugin-react-oxc": "^0.4.3",
     "openapi-typescript": "^7.13.0",
     "tailwindcss": "^4",
     "typescript": "^5",