docs: add hierarchical AGENTS.md knowledge base

- Update root AGENTS.md with regenerative content (144 lines, telegraphic)
- Add pkgs/AGENTS.md for package registry conventions (33 lines)
- Add docs/AGENTS.md for documentation structure (34 lines)
- All files follow telegraphic style, no redundancy with parent
- Preserves existing modules/home-manager/AGENTS.md

Hierarchy:
  ./AGENTS.md (root)
  ├── pkgs/AGENTS.md
  ├── docs/AGENTS.md
  └── modules/home-manager/AGENTS.md (existing)

pkgs/mem0/default.nix

@@ -0,0 +1,99 @@
+{
+  lib,
+  python3,
+  fetchFromGitHub,
+}:
+python3.pkgs.buildPythonPackage rec {
+  pname = "mem0ai";
+  version = "1.0.0";
+  pyproject = true;
+
+  src = fetchFromGitHub {
+    owner = "mem0ai";
+    repo = "mem0";
+    rev = "v${version}";
+    hash = "sha256-DluzIhwL/GanqtRSMW7ax+OVc2kZjbwQ0lpPCQFnD58=";
+  };
+
+  # Relax Python dependency version constraints
+  # mem0 has strict version pins that may not match nixpkgs versions
+  pythonRelaxDeps = true;
+
+  build-system = with python3.pkgs; [
+    hatchling
+  ];
+
+  dependencies = with python3.pkgs; [
+    litellm
+    qdrant-client
+    pydantic
+    openai
+    posthog
+    pytz
+    sqlalchemy
+    protobuf
+    uvicorn
+    fastapi
+  ];
+
+  optional-dependencies = with python3.pkgs; {
+    graph = [
+      # Note: some graph dependencies may not be available in nixpkgs
+      # neo4j is available, others will need to be packaged separately
+    ];
+    vector_stores = [
+      # chromadb  # available in nixpkgs
+      # pinecone-client  # may need packaging
+      # weaviate-client  # may need packaging
+      # faiss  # available as faiss-cpu
+      psycopg
+      pymongo
+      pymysql
+      redis
+      elasticsearch
+    ];
+    llms = [
+      groq
+      openai
+      # together  # may need packaging
+      # litellm  # may need packaging
+      # ollama  # may need packaging
+      # google-generativeai  # may need packaging
+    ];
+    extras = [
+      boto3
+      # langchain-community  # may need packaging
+      # sentence-transformers  # may need packaging
+      elasticsearch
+      # fastembed  # may need packaging
+    ];
+  };
+
+  # Skip tests for now since they require additional test dependencies
+  doCheck = false;
+
+  # Disable imports check because mem0 tries to create directories at import time
+  # which fails in the Nix sandbox (/homeless-shelter)
+  pythonImportsCheck = [];
+
+  postInstall = ''
+    install -Dm755 ${./server.py} $out/bin/mem0-server
+  '';
+
+  meta = with lib; {
+    description = "Long-term memory layer for AI agents with REST API support";
+    longDescription = ''
+      Mem0 provides a sophisticated memory layer for AI applications, offering:
+      - Memory management for AI agents (add, search, update, delete)
+      - REST API server for easy integration
+      - Support for multiple vector storage backends (Qdrant, Chroma, etc.)
+      - Graph memory capabilities
+      - Multi-modal support
+      - Configurable LLM and embedding models
+    '';
+    homepage = "https://github.com/mem0ai/mem0";
+    changelog = "https://github.com/mem0ai/mem0/releases/tag/v${version}";
+    license = licenses.asl20;
+    platforms = platforms.linux;
+  };
+}