expose underlying error on embedding failure (#7743)

Avoid a round-trip asking users for logs to see what went wrong.

server/routes.go

@@ -507,7 +507,7 @@ func (s *Server) EmbeddingsHandler(c *gin.Context) {
 	embedding, err := r.Embedding(c.Request.Context(), req.Prompt)
 	if err != nil {
 		slog.Info(fmt.Sprintf("embedding generation failed: %v", err))
-		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to generate embedding"})
+		c.JSON(http.StatusInternalServerError, gin.H{"error": fmt.Errorf("failed to generate embedding: %v", err)})
 		return
 	}