feat(build): Remove 'index' fallback to enable proper dynamic chunking

[AntonioVentilii]

Motivation

This change removes the 'index' fallback in the Vite manualChunks configuration. Returning undefined lets Rollup handle chunk splitting automatically, allowing dynamic imports (like i18n JSON files) to be bundled separately instead of being merged into a single large index chunk.

Before --> 2 chunks (biggest 5.4 MB)

After --> 168 chunks (biggest 2.1 MB)

[Copilot]

Pull Request Overview

This PR modifies the Vite build configuration to enable proper dynamic chunking by removing the default 'index' fallback in the manualChunks function. By returning undefined instead of 'index', Rollup can automatically handle chunk splitting, allowing dynamically imported resources (such as i18n JSON files) to be bundled into separate chunks rather than being combined into a single large index chunk.

Key Changes:

• Removed the 'index' fallback return value in the manualChunks configuration, replacing it with an implicit undefined return

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[AntonioVentilii]

Superseded by:

• feat(build): Remove manual chunks from Vite configs #9839

[AntonioVentilii]

Reopening this PR, since we require smarter chunks

[peterpeterparker]

Are you sure? I would have expected an exception for the languages, hasn't this for side effect to chunks the entire OISY code base?