Function finalize_spec 

pub fn finalize_spec(
    spec: &mut Spec,
    spec_repo: &FileSpecRepository,
    config: &Config,
    all_specs: &[Spec],
    options: FinalizeOptions,
) -> Result<()>

Finalize a spec after successful completion.

This is the canonical finalization logic with full validation:

• Checks for uncommitted changes in worktree
• Validates driver/member relationships
• Detects commits (if not provided)
• Checks agent co-authorship for approval requirements
• Updates status, commits, completed_at, and model
• Verifies persistence

This function is idempotent and can be called multiple times safely.