feat(742): Add feature specification for sample markdown document

[blackpc]

Summary

This PR adds the feature specification files for feature #742, which creates a markdown document.

Changes

• spec.yaml: Feature specification with problem statement, success criteria, and implementation details
• feature.yaml: Feature lifecycle metadata tracking the research phase
• test-c8e3e3.md: Sample markdown document with a title and descriptive content about markdown

Context

This completes the feature specification for creating a simple markdown document called test-c8e3e3.md with a title and 2-3 sentences describing a topic.

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