1.2.9

feat: support output dimensions for embedding models (#490) (#522)

Add optional outputDimension field for embedding models to request
specific dimensions from providers that support Matryoshka
Representation Learning (MRL).

Supported providers:
- OpenAI text-embedding-3-* (via 'dimensions' parameter)
- Google gemini-embedding-001 (via 'config.outputDimensionality')

Changes:
- Add outputDimension field to EmbeddingModel type
- Update all provider getEmbedding methods to accept dimensions option
- Add Output Dimensions input field in Add Embedding Model modal
- Validate that returned dimension matches requested outputDimension