API Installation Options and Documentation Improvements

[ParisNeo]

Changes

This PR introduces several improvements to the installation process and documentation:

1. Added API support as an optional installation feature:

   • Added extras_require for API dependencies
   • Separated core and API requirements
   • Made API installation optional using pip install "lightrag-hku[api]"

2. Reorganized API implementation:

   • Created proper entry points for all servers
   • Added consistent command-line interface
   • Improved server configuration options

3. Unified documentation in README.md:

   • Combined all API documentation
   • Added clear installation instructions
   • Included comprehensive configuration options
   • Added detailed usage examples
   • Documented automatic vectorization features

Benefits

• Cleaner installation process
• Reduced dependencies for users who don't need API
• Better organized codebase
• Improved documentation and examples
• Clearer API usage instructions

Testing

• Tested installation with and without API support
• Verified all entry points work correctly
• Confirmed documentation accuracy
• Tested automatic vectorization features

Notes

This PR improves the overall user experience by making the API optional and providing clearer documentation while maintaining all existing functionality.