Add MCP server for Claude Code memory integration

- Create stdio MCP server wrapping core memory functions (query, show, list, children, add, link)
- Add CLAUDE.md with memory-querying instructions for Claude
- Register MCP server in .mcp.json
- Document MCP setup and tools in USAGE.md

USAGE.md

@@ -260,3 +260,44 @@ The web server exposes these endpoints under `/api`:
 | `DELETE` | `/api/edges/:id` | Delete edge |
 | `GET` | `/api/graph` | Get full graph (nodes + edges) for visualization |
 | `POST` | `/api/search` | Search. Body: `{ text, options?: { kind?, tags?, limit?, includeStale? } }` |
+
+---
+
+## MCP Server (Claude Code Integration)
+
+Cortex includes an MCP (Model Context Protocol) server that exposes memory tools directly to Claude Code.
+
+### Setup
+
+1. Build the project: `npm run build`
+2. Ensure `.mcp.json` exists in the project root:
+
+```json
+{
+  "mcpServers": {
+    "memory": {
+      "command": "node",
+      "args": ["./dist/mcp/index.js"]
+    }
+  }
+}
+```
+
+3. Restart Claude Code — the memory tools will appear automatically.
+
+### MCP Tools
+
+| Tool | Description | Parameters |
+|---|---|---|
+| `memory_query` | Hybrid search (BM25 + vector + freshness) | `text`, `kind?`, `limit?` |
+| `memory_show` | Show node by ID or prefix with connections | `id` |
+| `memory_list` | List nodes with filters | `kind?`, `status?`, `tags?`, `limit?` |
+| `memory_children` | List children of a node | `id`, `kind?` |
+| `memory_add` | Add a new node | `kind`, `title`, `content?`, `tags?`, `status?`, `sections?` |
+| `memory_link` | Create an edge between nodes | `fromId`, `toId`, `type` |
+
+### Manual Testing
+
+```bash
+echo '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2024-11-05","capabilities":{},"clientInfo":{"name":"test","version":"0.1"}}}' | node dist/mcp/index.js
+```