refactor(packages): rename rules-core to rules-engine

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

packages/agents-md-core/src/finder.ts

@@ -1,6 +1,6 @@
 import {
   findAgentsMdUp as findAgentsMdUpCore,
-} from "@oh-my-opencode/rules-core";
+} from "@oh-my-opencode/rules-engine";
 import { isAbsolute, resolve } from "node:path";
 
 import type { AgentsMdDiscoveryInput } from "./types";