move playground ui to llama-stack repo (#536)

# What does this PR do?

- Move Llama Stack Playground UI to llama-stack repo under
llama_stack/distribution
- Original PR in llama-stack-apps:
https://github.com/meta-llama/llama-stack-apps/pull/127

## Test Plan
```
cd llama-stack/llama_stack/distribution/ui
streamlit run app.py
```


## Before submitting

- [ ] This PR fixes a typo or improves the docs (you can dismiss the
other checks if that's the case).
- [ ] Ran pre-commit to handle lint / formatting issues.
- [ ] Read the [contributor
guideline](https://github.com/meta-llama/llama-stack/blob/main/CONTRIBUTING.md),
      Pull Request section?
- [ ] Updated relevant documentation.
- [ ] Wrote necessary unit or integration tests.

llama_stack/distribution/ui/modules/api.py

@@ -0,0 +1,41 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the terms described in the LICENSE file in
+# the root directory of this source tree.
+
+import os
+
+from typing import Optional
+
+from llama_stack_client import LlamaStackClient
+
+
+class LlamaStackEvaluation:
+    def __init__(self):
+        self.client = LlamaStackClient(
+            base_url=os.environ.get("LLAMA_STACK_ENDPOINT", "http://localhost:5000"),
+            provider_data={
+                "fireworks_api_key": os.environ.get("FIREWORKS_API_KEY", ""),
+                "together_api_key": os.environ.get("TOGETHER_API_KEY", ""),
+                "openai_api_key": os.environ.get("OPENAI_API_KEY", ""),
+            },
+        )
+
+    def list_scoring_functions(self):
+        """List all available scoring functions"""
+        return self.client.scoring_functions.list()
+
+    def list_models(self):
+        """List all available judge models"""
+        return self.client.models.list()
+
+    def run_scoring(
+        self, row, scoring_function_ids: list[str], scoring_params: Optional[dict]
+    ):
+        """Run scoring on a single row"""
+        if not scoring_params:
+            scoring_params = {fn_id: None for fn_id in scoring_function_ids}
+        return self.client.scoring.score(
+            input_rows=[row], scoring_functions=scoring_params
+        )