feat: opt-in aggregate research consent at account creation

[ibloud]

Summary

Add plain-language consent toggle (default OFF) for aggregate research usage.

Implementation

• Add account creation toggle:
  • researchConsent: false by default
• Ensure aggregator/export paths:
  • include only anonymized post-game summaries for consented users
  • never export raw move logs
• Persist consent in playerProfiles.

Acceptance Criteria

• Consent flag is stored and respected end-to-end.
• Non-consented users are excluded from aggregate research outputs.
• Raw matchLogs are never included in research exports.