feat: Add task-aware embedding support

[StoreksFeed]

Description

Modern embedding models (e.g., Gemini and FRIDA) support asymmetric embeddings through task-specific prefixes, which significantly improve retrieval accuracy by generating different embeddings for queries versus documents. This PR implements this capability in LightRAG.

Related Issues

N/A

Changes Made

Configuration & Documentation

• Added EMBEDDING_DOCUMENT_PREFIX and EMBEDDING_QUERY_PREFIX environment variables to lightrag/api/config.py
• Updated docs/DockerDeployment.md and env.example with new configuration options
• Added example demonstrating prefix usage: examples/unofficial-sample/lightrag_embedding_prefixes.py

Core Infrastructure

• Enhanced EmbeddingFunc wrapper in lightrag/utils.py with supports_context parameter
• Updated wrap_embedding_func_with_attrs decorator to support context-aware functions
• Modified lightrag/operate.py to pass context

Vector Storage Backends

Updated all storage implementations to use context parameter:

• lightrag/kg/faiss_impl.py
• lightrag/kg/milvus_impl.py
• lightrag/kg/mongo_impl.py
• lightrag/kg/nano_vector_db_impl.py
• lightrag/kg/postgres_impl.py
• lightrag/kg/qdrant_impl.py

LLM Provider Bindings

Updated embedding functions with context support:

• lightrag/llm/openai.py - Prefix support
• lightrag/llm/ollama.py - Prefix support
• lightrag/llm/gemini.py - Automatic task_type selection
• lightrag/llm/jina.py - Automatic task selection
• lightrag/llm/hf.py - Prefix support

Binding Options

• Updated GeminiEmbeddingOptions to support automatic task_type selection

API Server

• Integrated prefix configuration into lightrag/api/lightrag_server.py
• Updated lightrag/api/utils_api.py splash screen to display prefix settings

Checklist

• Changes tested locally
• Code reviewed
• Documentation updated (if necessary)
• Unit tests added (if applicable)

Additional Notes

Backward Compatibility

• Fully backward compatible - task is not injected unless explicitly asked
• Existing deployments without prefix configuration should continue to work unchanged
• Optional feature activated only when EMBEDDING_DOCUMENT_PREFIX or EMBEDDING_QUERY_PREFIX environment variables are set