Implement Soroban Contract Documentation Extractor

[mijinummi]

🧠 Concept

Extract documentation embedded within contracts.

⚠️ Problem

Documentation is difficult to consolidate across projects.

📁 Implementation Scope

• src/extractors/docs/stellar/

✅ Requirements

• Parse comments and annotations
• Generate documentation summaries
• Export structured outputs

🎯 Acceptance Criteria

• Documentation extraction implemented
• Summaries generated successfully