docs: add ElizaOS vs Anthropic Skills comparative analysis

Add comprehensive analysis comparing ElizaOS plugin architecture with
Anthropic's Agent Skills system to identify framework improvement opportunities.

Key findings:
- ElizaOS excels at type-safety, action chaining, and stateful services
- Skills excels at simplicity, progressive disclosure, and portability
- Proposed enhancements: LitePlugins/Instructions, ScriptExecutorService,
  progressive loading, and simplified CLI

Includes prototype implementations for all proposed enhancements.

Author: claude