feat: add lightrag-mcp MCP server + agent tooling

- Add AGENTS.md with repo guidelines
- Add lightrag-mcp: FastMCP server exposing insert_documents() + query_documents()
  to LLM agents via stdio transport, talks to LightRAG REST API
- Add scripts/patch-vllm-cpu.py for CPU inference patching
- Add .env.vllm for vLLM configuration
- Update flake.nix with expanded dev shell
- Update .env.lightrag
- Remove CLAUDE.md (replaced by AGENTS.md)

lightrag-mcp/pyproject.toml

@@ -0,0 +1,11 @@
+[project]
+name = "lightrag-mcp"
+version = "0.1.0"
+description = "Add your description here"
+readme = "README.md"
+requires-python = ">=3.10"
+dependencies = [
+    "fastmcp>=3.2.4",
+    "httpx>=0.28.1",
+    "lightrag-hku>=1.4.15",
+]