fix(ollama): Download remote image URLs for Ollama (#2551)

## What does this PR do?

Ollama does not support remote images. Only local file paths OR base64
inputs are supported. This PR ensures that the Stack downloads remote
images and passes the base64 down to the inference engine.

## Test Plan

Added a test cases for Responses and ran it for both `fireworks` and
`ollama` providers.

llama_stack/providers/remote/inference/ollama/ollama.py

@@ -5,6 +5,7 @@
 # the root directory of this source tree.
 
 
+import base64
 import uuid
 from collections.abc import AsyncGenerator, AsyncIterator
 from typing import Any
@@ -77,6 +78,7 @@ from llama_stack.providers.utils.inference.prompt_adapter import (
     content_has_media,
     convert_image_content_to_url,
     interleaved_content_as_str,
+    localize_image_content,
     request_has_media,
 )
 
@@ -496,6 +498,21 @@ class OllamaInferenceAdapter(
         user: str | None = None,
     ) -> OpenAIChatCompletion | AsyncIterator[OpenAIChatCompletionChunk]:
         model_obj = await self._get_model(model)
+
+        # Ollama does not support image urls, so we need to download the image and convert it to base64
+        async def _convert_message(m: OpenAIMessageParam) -> OpenAIMessageParam:
+            if isinstance(m.content, list):
+                for c in m.content:
+                    if c.type == "image_url" and c.image_url and c.image_url.url:
+                        localize_result = await localize_image_content(c.image_url.url)
+                        if localize_result is None:
+                            raise ValueError(f"Failed to localize image content from {c.image_url.url}")
+
+                        content, format = localize_result
+                        c.image_url.url = f"data:image/{format};base64,{base64.b64encode(content).decode('utf-8')}"
+            return m
+
+        messages = [await _convert_message(m) for m in messages]
         params = await prepare_openai_completion_params(
             model=model_obj.provider_resource_id,
             messages=messages,