P2E: calculate reward points from skill-based activity

[ilyar]

Source PRD: tasks/prd-full-play-to-earn.md
Parent epic: #86
PRD section: US-004

Description

Reward progress should come from server-authoritative skill/activity signals, not from one paid match.

Acceptance Criteria

• Reward points are derived from server-authoritative match settlement events.
• Base reward points use deterministic inputs such as win, draw, loss, score, rating delta, opponent rating band, and completed match count.
• Reward points are capped per day and per season to reduce grinding abuse.
• Forfeit, timeout, disconnect, and rematch farming rules are explicit.
• Matches against the same account pair have configurable daily reward caps.
• Reward points are idempotent per match/account/campaign.
• Tests cover win, draw, loss, clean win, forfeit, timeout, duplicate settlement, and repeated pair caps.

Constraints

• Keep current paid PvP settlement as entry fee, not player-funded prize pool.
• Do not make Season Points redeemable or refundable.
• Keep payout/compliance/provider secrets backend-only.
• Treat this as deferred future-phase work until mechanics/self-host production readiness is stable.

Notes

Keep gameplay server-authoritative and do not let frontend allocate reward points.