feat: add voyage-4 model series and remove unused method

[BeamNawapat]

Summary

• Add voyage-4-large, voyage-4, voyage-4-lite, and voyage-4-nano to the VoyageAI supported models list (released January 2026)
• Remove unused updateDimensionForModel() which duplicated logic from updateModelSettings()

Changes

• packages/core/src/embedding/voyageai-embedding.ts — Add 4 voyage-4 models, remove dead method

Test plan

• pnpm build passes
• Existing VoyageAI models still work (no regression)

[Copilot]

Pull request overview

This PR updates the core VoyageAI embedding provider to recognize the newly released Voyage 4 model series and removes a redundant, unused dimension update helper.

Changes:

• Added voyage-4-large, voyage-4, voyage-4-lite, and voyage-4-nano to VoyageAIEmbedding.getSupportedModels().
• Removed the unused updateDimensionForModel() method (logic is already covered by updateModelSettings()).

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[Copilot]

voyage-4-nano lists a default dimension of 512, but updateModelSettings() currently hard-codes this.dimension = 1024 whenever modelInfo.dimension is a string. This will report the wrong dimension for voyage-4-nano (and can break downstream vector DB inserts if the embedding length is 512 but metadata says 1024). Consider representing the default dimension as a number (e.g., 512) or parsing the default from the dimension string (e.g., extracting the (... default) value) so per-model defaults are respected.

[zc277584121]

Clean split from #305 — exactly what was needed. The voyage-4 model data looks correct, and removing the duplicate updateDimensionForModel is a good cleanup since updateModelSettings already covers the same logic.

LGTM.