[experiment] Migrate tooling to Vite+

[Juice10]

Summary

• add Vite+ workspace tooling config for format and lint
• migrate Vite/Vitest imports to vite-plus and vite-plus/test
• replace Prettier/Oxfmt and legacy ESLint config with Vite+ driven formatting plus ESLint flat config
• update format CI to run the repo-local Vite+ CLI
• keep the existing vite.config.default.ts package build factory in place

Notes

• package build configs still import vite.config.default.ts; the new root vite.config.ts is only for Vite+ workspace tooling blocks
• packageManager is bumped to yarn@1.22.22 so vp install can resolve a published Yarn Classic version while the repo-local yarnPath remains in place
• Vite+ type checking is disabled for now because the current workspace has pre-existing TypeScript/tsconfig issues under the stricter checker; existing yarn check-types remains the type-check path

Validation

• vp install --ignore-scripts --frozen-lockfile
• vp check
• vp test run packages/packer/test/packer.test.ts

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Latest commit: 1471ebe

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[github-actions]

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