chore: consolidate essential fixes and add pre-commit hooks

- Add pre-commit configuration with ruff and black
- Fix lint CI job to use uv tool install instead of sync
- Add essential LlamaIndex dependencies to leann-core

Co-Authored-By: Yichuan Wang <73766326+yichuan-w@users.noreply.github.com>

packages/leann-core/pyproject.toml

@@ -20,6 +20,8 @@ dependencies = [
     "torch>=2.0.0",
     "sentence-transformers>=2.2.0",
     "llama-index-core>=0.12.0",
+    "llama-index-readers-file>=0.4.0",  # Essential for document reading
+    "llama-index-embeddings-huggingface>=0.5.5",  # For embeddings
     "python-dotenv>=1.0.0",
     "openai>=1.0.0",
     "huggingface-hub>=0.20.0",