fix: replace bare string raises with proper exception types (#22446)

`raise "string"` in Python raises TypeError instead of the intended
error, making error messages confusing and debugging difficult.

Co-authored-by: gambletan <ethanchang32@gmail.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

backend/open_webui/routers/ollama.py

@@ -1747,7 +1747,7 @@ async def download_file_stream(
 
                                 yield f"data: {json.dumps(res)}\n\n"
                             else:
-                                raise "Ollama: Could not create blob, Please try again."
+                                raise RuntimeError("Ollama: Could not create blob, Please try again.")
 
 
 # url = "https://huggingface.co/TheBloke/stablelm-zephyr-3b-GGUF/resolve/main/stablelm-zephyr-3b.Q2_K.gguf"