refactor(users): remove dead analytics endpoints and consolidate into profile

Summary

• Removed 3 dead endpoints with zero consumers (frontend, CLI, and tests show no usage):
  • GET /{id}/edit-activity
  • GET /{id}/edit-metrics
  • GET /{id}/activity-summary
• Added average_edits_per_record to GET /{id}/profile?include=summary under summary.edits — the only field not already present in the profile endpoint
• Removed UserEditActivity and UserEditMetrics schemas from record_history.py and __init__.py
• Net result: -163 lines, no data loss, no breaking changes

Test plan

• GET /{id}/profile?include=summary → summary.edits.average_edits_per_record present
• GET /{id}/edit-activity → 404 Not Found
• GET /{id}/edit-metrics → 404 Not Found
• GET /{id}/activity-summary → 404 Not Found

Checklist

• Code follows project API guidelines
• Documentation is updated (OpenAPI docs reflect removed endpoints)
• Code adheres to project coding standards

Closes #121