Add migration validation reports for legacy-to-Sprocket parity

[gankoji]

Summary

Build repeatable validation reports that compare legacy MLEDB state to Sprocket state during the write-parity and backfill phases.

Why

This migration touches permissions, accounts, rosters, staff assignments, suspensions, and scheduling. We need durable parity checks before removing legacy reads/writes.

Scope

• Add validation reports for at least:
  • org-team permission assignments
  • player/account mappings
  • roster counts by team/league
  • staff/captain assignments
  • suspension / restricted-player state
  • scheduled match times
• Make the reports easy to rerun during backfill and cutover.
• Surface mismatches in a form that can drive remediation.

Acceptance criteria

• Validation can be run repeatedly during migration.
• The report output clearly identifies parity mismatches.
• Each migrated domain has a corresponding parity check.
• Cutover decisions can be based on objective validation rather than spot checks.