AI/prompt-aware wrapping preservation

[kafkade]

Summary

Per ADR-009, add AI/prompt-aware content preservation.

Features

1. Preserve AI-marker fenced blocks (prompt, copilot, ai, system, user, assistant)
2. Configurable preserved-block markers: lumpia.preserveBlocks
3. AI-tagged comment handling (// AI:, // prompt:) with hanging indent
4. Natural Markdown support for .github/copilot-instructions.md

Acceptance Criteria

• AI code fence languages treated as no-wrap
• lumpia.preserveBlocks setting for custom markers
• AI-tagged comments wrap with preserved tag prefix
• Golden test fixtures for AI comment patterns

References

• ADR-009: AI/Prompt-Aware Wrapping

[kafkade]

Semver impact: Minor (0.x.0)

Adds AI/prompt-aware content preservation — new preserved-block markers and AI-template detection. Purely additive; existing wrapping behavior for non-AI content is unchanged.