feat(vector_store): add QdrantVectorStore implementation

- Add QdrantVectorStore class with full async support
- Implement all vector store methods for Qdrant backend
- Add documentation and examples for Qdrant integration
- Update vector store comparison table in docs
- Add qdrant_client dependency to reme optional dependencies
- Update version to 0.1.11.3 in pyproject.toml and __init__.py
- Remove unused imports and environment loading from multiple files

Author: jinliyl

README.md

@@ -9,7 +9,7 @@
 
 <p align="center">
   <a href="https://pypi.org/project/flowllm/"><img src="https://img.shields.io/badge/python-3.12+-blue" alt="Python Version"></a>
-  <a href="https://pypi.org/project/flowllm/"><img src="https://img.shields.io/badge/pypi-v0.1.10-blue?logo=pypi" alt="PyPI Version"></a>
+  <a href="https://pypi.org/project/flowllm/"><img src="https://img.shields.io/badge/pypi-v0.1.11.3-blue?logo=pypi" alt="PyPI Version"></a>
   <a href="./LICENSE"><img src="https://img.shields.io/badge/license-Apache--2.0-black" alt="License"></a>
 </p>