Update inspect and contracts tooling for structure slots features

Acceptance Criteria

• refrakt inspect output shows slot assignments when a rune config declares slots
• refrakt inspect visualizes projection effects (shows before/after tree when projection is active)
• refrakt inspect --audit flags new BEM selectors created by projection group entries
• refrakt contracts includes slot ordering in structure contracts
• refrakt contracts includes projection declarations and warns on invalid data-name references (targeting a data-name that doesn't exist in the rune's output)
• refrakt contracts --check catches drift from slot/projection changes
• All existing CLI tests pass

Approach

1. Update the inspect renderer to show slot groupings in the HTML output
2. Add projection visualization — when projection is configured, show the tree before and after the projection pass
3. Update the contracts generator to include slot order and projection declarations in the JSON output
4. Add validation for projection data-name references against the rune's known output contract
5. Update the audit logic to account for group-generated BEM selectors

References

• Structure Slots and Declarative Flexibility (Contracts and Tooling section)
• Implement named slots with ordering for structure entries (slots)
• Implement element projection (hide, group, relocate) (projection)