Feature Request: Support skills for goose-android-agent

Like https://github.com/google-ai-edge/gallery/tree/main/skills.

The issue references the Google AI Edge gallery skills directory. Start by examining the goose-android-agent codebase to understand its current architecture and how skills are implemented in the referenced gallery. Look for existing agent modules or extension points. Determine what 'support skills' entails—likely adding a plugin system or integrating pre-built skill modules. Check for any tests related to agent functionality to understand the expected behavior.

Written by the indexing model from the issue text.