feat(plugin): Add dispose() method to Hooks interface

Add optional dispose callback to plugin Hooks interface to allow
plugins to clean up resources when the Instance is disposed.

Author: sauerdaniel

packages/plugin/src/index.ts

@@ -231,4 +231,8 @@ export interface Hooks {
    * Modify tool definitions (description and parameters) sent to LLM
    */
   "tool.definition"?: (input: { toolID: string }, output: { description: string; parameters: any }) => Promise<void>
+  /**
+   * Called when the plugin is being disposed/cleaned up
+   */
+  dispose?: () => Promise<void>
 }