Add initial implementation of txt2graph tool for knowledge graph generation

- Created a new Streamlit application for visualizing knowledge graphs.
- Implemented text extraction from PDF, Markdown, and TXT files.
- Developed graph building logic using Zep Cloud API.
- Added support for custom entity types and relationships.
- Included interactive HTML visualization for generated graphs.
- Updated .gitignore to include new directories and files.
- Added example environment configuration file (.env.example) for API key setup.
- Created README.md with installation and usage instructions.
- Introduced various utility scripts and styles for enhanced functionality.

txt2graph/requirements.txt

@@ -0,0 +1,18 @@
+# Zep Cloud SDK
+zep-cloud>=2.0.0
+
+# PDF处理
+PyMuPDF>=1.24.0
+
+# Markdown处理
+markdown>=3.5.0
+
+# Web可视化界面
+streamlit>=1.38.0
+
+# 图可视化
+pyvis>=0.3.2
+
+# 环境变量
+python-dotenv>=1.0.0
+