feat: add vite-layers

vite-layers/test/fixtures/stack/app/app.config.ts

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+export default { name: 'app', extends: ['../base'], features: { shared: 'app', app: true } }

vite-layers/test/fixtures/stack/base/app.config.ts

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+export default { name: 'base', extends: ['../core'], features: { shared: 'base', base: true } }

vite-layers/test/fixtures/stack/core/app.config.ts

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+export default { name: 'core', features: { shared: 'core', core: true }, vite: { define: { LVL: '"core"' } } }