feat: Support skills like MAF or ADK-Go

[MAF]
https://github.com/microsoft/agent-framework-go/tree/main/agent/skills

[ADK-Go]
https://github.com/google/adk-go/tree/main/tool/skilltoolset/skill

The issue asks to support skills from MAF and ADK-Go frameworks. Start by examining the linked repositories to understand their skill interfaces and how they are structured. Look in the rig codebase for existing skill integration points or modules. Determine what changes are needed to import or adapt these external skill definitions. 'Done' means rig can use skills defined in those frameworks.

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