fix: restore lmstudio/deepseek providers in TS factory, add langchain to extras

- Restore LMStudioEmbedder, LMStudioLLM, DeepSeekLLM in TS factory.ts
  (accidentally removed during graph store cleanup — unrelated to graphs)
- Add langchain>=0.1.0 to Python extras dep group (was transitively
  provided by langchain-neo4j in the removed graph group, still needed
  by mem0/llms/langchain.py and mem0/embeddings/langchain.py)
- Add pytest.importorskip("langchain") to test_langchain.py for graceful
  skip when langchain isn't installed

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/llms/test_langchain.py

@@ -2,6 +2,8 @@ from unittest.mock import Mock
 
 import pytest
 
+pytest.importorskip("langchain", reason="langchain not installed")
+
 from mem0.configs.llms.base import BaseLlmConfig
 from mem0.llms.langchain import LangchainLLM