Extract Shared Layout Meta Tag Utility

Summary

Runes that extend SplitLayoutModel all emit identical boilerplate for layout meta tags (layout, ratio, valign, gap, collapse). Extract this into a shared utility in @refrakt-md/runes so each rune's transform calls one function instead of copy-pasting the conditional logic.

Acceptance Criteria

• New buildLayoutMetas() utility exported from packages/runes/src/common.ts (or a new layout-helpers.ts)
• Utility accepts the split layout attrs object and returns { metas: Tag[], properties: Record<string, Tag> }
• Handles the layout !== 'stacked' guard, gap/collapse conditionals, and all five meta tags (layout, ratio, valign, gap, collapse)
• recipe.ts in @refrakt-md/learning refactored to use the shared utility
• realm.ts and faction.ts in @refrakt-md/storytelling refactored to use the shared utility
• playlist.ts in @refrakt-md/media refactored to use the shared utility
• All existing tests pass — no change to identity transform output

Approach

1. Study the layout meta tag block in recipe.ts (reference implementation) and compare with realm.ts, faction.ts, playlist.ts
2. Extract the shared pattern into a utility function
3. Replace the inline blocks in all four runes with calls to the utility
4. Run tests to verify output is unchanged

References

• Rune Output Standards (Standard 6 — Layout Meta Tag Emission Should Be Shared)