chore(deps): upgrade vite to v8 and @vitejs/plugin-react to v6

[jinglemansweep]

Summary

Upgrade Vite from v6 to v8 and @vitejs/plugin-react from v4 to v6. These two are mutually dependent (plugin-react@6 requires vite@^8 peer, and plugin-react@4 doesn't support vite@8) and must land together.

Supersedes and closes #329 and #331.

Changes

Dependency bumps (package.json, package-lock.json)

• vite: ^6 -> ^8.1.5 (resolved: 8.1.5)
• @vitejs/plugin-react: ^4 -> ^6.0.4 (resolved: 6.0.4)

Vite config migration (vite.config.ts)

Vite 8 replaces Rollup with Rolldown as the bundler engine. Two breaking changes required config migration:

1. build.rollupOptions -> build.rolldownOptions (rollupOptions is a deprecated alias)

2. Object-form manualChunks removed -> migrated to Rolldown's codeSplitting.groups API:

   // Before (Rollup object form - removed in Vite 8)
   manualChunks: {
     vendor: ["react", "react-dom", "react-router"],
     i18n: ["i18next", "react-i18next", "i18next-browser-languagedetector"],
   }
   
   // After (Rolldown codeSplitting.groups)
   codeSplitting: {
     groups: [
       { name: "vendor", test: /[\\/]node_modules[\\/](react|react-dom|react-router)[\\/]/ },
       { name: "i18n", test: /[\\/]node_modules[\\/](i18next|react-i18next|i18next-browser-languagedetector)[\\/]/ },
     ],
   }

Why the Renovate PRs failed

• chore(deps): update dependency @vitejs/plugin-react to v6 #329 (plugin-react@6): ERESOLVE — plugin-react@6 requires vite@^8 peer dep, but project had vite@^6
• chore(deps): update dependency vite to v8 #331 (vite@8): EUSAGE — Renovate failed to regenerate package-lock.json ("Artifact update problem"), and plugin-react@4 doesn't support vite@8

Build output

Chunks produced by the new codeSplitting config:

• vendor: 230 KB (react, react-dom, react-router)
• i18n: 55 KB (i18next, react-i18next, i18next-browser-languagedetector)

Verification

• npm run build — succeeds (Tailwind + Vite/Rolldown)
• npx tsc --noEmit — clean
• npm run test:frontend (vitest) — 339/339 passing
• pre-commit run --all-files — all green

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ All tests successful. No failed tests found.

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