feat: add multi-model cleanup tool and CLI command

- Bump `@opencode-ai/plugin` dependency from 1.2.27 to 1.3.0.
- Introduce `cleanup` command in CLI with force and remote options.
- Export `cleanupMultiModel` from core index.
- Register `multi-model-cleanup` tool in plugin and update exports.
- Add `CleanupOptions` and `CleanupResult` types to define cleanup behavior and results.

src/core/index.ts

@@ -1,3 +1,4 @@
+export { cleanupMultiModel } from "./cleanup";
 export { closeMultiModel } from "./close";
 export { openMultiModel } from "./open";
 export * from "./utils";