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

.mcp.json

@@ -0,0 +1,8 @@
+{
+  "mcpServers": {
+    "memory": {
+      "command": "node",
+      "args": ["./dist/mcp/index.js"]
+    }
+  }
+}