Update frontend build dependencies for esbuild advisory

[Vedasheersh]

Summary

• Update the frontend Vite toolchain from Vite 6 to Vite 8 and @vitejs/plugin-vue 6.
• Refresh package-lock.json so the frontend no longer installs the vulnerable esbuild range reported by GHSA-gv7w-rqvm-qjhr.
• The refreshed lockfile also resolves the transitive PostCSS audit finding by using postcss@8.5.15.

Verification

• npm audit --json reports 0 vulnerabilities.
• npm run build succeeds with Vite 8.0.16.
• git -c core.whitespace=blank-at-eol,blank-at-eof,space-before-tab,cr-at-eol diff --check