P2E: maintain no-purchase eligibility path

[ilyar]

Source PRD: tasks/prd-full-play-to-earn.md
Parent epic: #86
PRD section: US-005

Description

Campaigns may require a no-purchase path so rewards are not automatically tied to paid entry.

Acceptance Criteria

• Campaign config supports no_purchase_required=true.
• Eligible free/demo route is documented per campaign.
• Free route can earn reward points under explicit caps and anti-abuse rules.
• Paid ELM purchase is never described as required to earn a prize unless legal review approves that specific campaign structure.
• UI shows eligibility requirements before a user starts earning.
• Tests cover paid user, free user, ineligible user, and blocked jurisdiction cases.

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

This is a compliance/product gate, not a gameplay shortcut.