[Feature] Moderation panel — edit player ELO

## Overview
Moderators can edit a player's ELO rating directly from the moderation panel. Used for corrections after exploits, bugs, or confirmed cheating. All ELO edits must be logged with reason.

## Scope
- Edit ELO field on any player profile from moderation panel
- Mandatory reason field when editing ELO
- Full audit log: moderator ID, player ID, previous ELO, new ELO, reason, timestamp
- Audit log viewable by admins (not moderators)
- ELO change takes effect immediately

## Acceptance criteria
- [ ] Moderator can edit ELO from player profile in moderation panel
- [ ] Reason field is mandatory — cannot submit without it
- [ ] Audit log entry created on every ELO change
- [ ] Audit log contains: moderator ID, player ID, old ELO, new ELO, reason, timestamp
- [ ] Audit log visible to admins only
- [ ] ELO change reflected immediately in game and on leaderboard

## Security notes
- Moderators cannot edit their own ELO
- ELO edits should trigger an internal alert if change exceeds a threshold (e.g. ±500)

## Dependencies
- **Depends on:** Moderator role (#ROLE), Player search (#SEARCH)