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/injector.ts

@@ -1,4 +1,4 @@
-import type { AgentsMdCache } from "@oh-my-opencode/rules-core";
+import type { AgentsMdCache } from "@oh-my-opencode/rules-engine";
 import { promises as fsPromises } from "node:fs";
 import { dirname } from "node:path";