feat(pipeline): add automated skill export bridge from verified memory patterns

[harshsinghmp]

Classification

actionable-feature

Context & Rationale

When a learning or invariant in musememory demonstrates high recurrence and verified impact across multiple client repositories, it should be easily exported into a reusable Agent Skill for muse-skills or skills.

Key Capabilities & Scope

1. Provide CLI command: memory export-skill <pattern-key> --name <skill-name>.
2. Format the memory cluster into RFC-compliant SKILL.md (YAML frontmatter + 5 required sections).
3. Validate that the exported skill is fully self-contained and free of proprietary credentials or private client paths.

Verification Criteria

• memory export-skill outputs a valid Agent Skill directory.
• Passes test suite (bun test test/).