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)

.env.lightrag

@@ -1,18 +1,19 @@
-# LLM via Ollama
-LLM_BINDING=ollama
-LLM_MODEL=qwen3:0.6b
-LLM_BINDING_HOST=http://localhost:11434
+LLM_BINDING=openai
+LLM_MODEL=minimax/minimax-m2.7
+LLM_BINDING_HOST=https://openrouter.ai/api/v1
+LLM_BINDING_API_KEY=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
 
-# Embeddings via Ollama
+# Embeddings via Ollama (port 11434)
 EMBEDDING_BINDING=ollama
-EMBEDDING_MODEL=qwen3-embedding:0.6b
+EMBEDDING_MODEL=qwen3-embedding:4b
 EMBEDDING_BINDING_HOST=http://localhost:11434
-EMBEDDING_DIM=1024
+EMBEDDING_API_KEY=
+EMBEDDING_DIM=2560
 
 # Storage (local files)
 RAG_DIR=./rag_storage
 
-# Timeouts (in seconds) — increase for large local models
+# Timeouts (in seconds)
 EMBEDDING_TIMEOUT=60
 TIMEOUT=60