fix(ollama): correctly parse nested embeddings array from ollama endpoint /api/embed

[CAPsMANyo]

Description

• Updates the OllamaEmbeddingResponse struct in src/llm/ollama.rs to match the Ollama API. It now expects embeddings: Vec<Vec> instead of embedding: Vec.
• Updates embed_text to take the first (index 0) embedding from the nested list.
• This api endpoint supports multiple inputs and returns a list of embeddings. This change assumes a single input (as required by the LlmEmbeddingClient trait) and parses the first embedding from the response.

Motivation and context

• The Ollama embedding client was broken because it couldn't parse the correct API response, causing "Invalid JSON" errors.
• This fix aligns the client with official Ollama documentation - https://docs.ollama.com/api#generate-embeddings

Is this a breaking change?

• No

Related GitHub issues

• [BUG] Ollama.rs expects incorrect response from /api/embed #1226

[badmonster0]

@CAPsMANyo thanks for the PR!!