Migrate community package postTransform uses to declarative config

Acceptance Criteria

• Beat rune (runes/storytelling/src/config.ts) — postTransform replaced with valueMap/mapTarget on the status modifier
• ComparisonRow rune (runes/marketing/src/config.ts) — postTransform replaced with valueMap/mapTarget
• Testimonial rune (runes/marketing/src/config.ts) — postTransform replaced with repeat on structure entry for star ratings
• refrakt inspect output is identical before and after for each migrated rune
• All existing tests pass
• CSS coverage tests pass (no selector regressions)
• The 4 remaining postTransform uses (genuinely complex cases) are untouched

Approach

1. For each rune, capture the current refrakt inspect output as a baseline
2. Replace the postTransform with the equivalent declarative config
3. Compare inspect output to confirm identical HTML
4. Run full test suite after each migration

References

• Structure Slots and Declarative Flexibility (Validation section)
• Add value mapping to modifier config (value mapping — enables Beat, ComparisonRow migration)
• Add repeated element generation to structure entries (repeated elements — enables Testimonial migration)