fix: embedding URL path missing /v1 prefix

The embedding endpoint path was  but OpenAI-compatible APIs
serve embeddings at . When EMBEDDING_BASE_URL is set to a
bare host (e.g. https://llm.aviron.ai), the resulting URL would be
/eembeddings instead of /v1/embeddings, returning 404.

Changed defaultBaseURL to not include /v1 and always use /v1/embeddings
as the endpoint path.

embed.go

@@ -12,7 +12,7 @@ import (
 )
 
 const defaultModel = "text-embedding-3-small"
-const defaultBaseURL = "https://api.openai.com/v1"
+const defaultBaseURL = "https://api.openai.com"
 
 type embedder struct {
 	apiKey     string
@@ -61,7 +61,7 @@ func (e *embedder) embedText(ctx context.Context, text string) ([]float32, error
 		return nil, fmt.Errorf("marshal embedding request: %w", err)
 	}
 
-	req, err := http.NewRequestWithContext(ctx, http.MethodPost, e.baseURL+"/embeddings", bytes.NewReader(body))
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, e.baseURL+"/v1/embeddings", bytes.NewReader(body))
 	if err != nil {
 		return nil, fmt.Errorf("create embedding request: %w", err)
 	}