Add EmbeddingProvider interface with OpenAI-compatible, local (optional
@xenova/transformers via dynamic import), and Noop (FTS5-only fallback)
implementations. EmbeddingService batches requests and persists Float32Array
blobs to snippet_embeddings. GET/PUT /api/v1/settings/embedding endpoints
read and write embedding config from the settings table.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
