Referrals: enable referral codes and credits on mobile (referrals flag)

[teetangh]

Context

referrals/ routes are gated (FeatureFlags.referrals = false); the consultant dashboard referral card is flag-hidden and the dashboard provider skips the gated endpoints.

Scope

1. Resolve the algorithm gaps in ChatGPT 5.4: Referral algorithm review: missing qualification loop, unsafe application flow, and unusable credit balances #52 first (qualification loop, credit application safety)
2. Re-audit against synced schema: Referral.organizationId (org attribution), ReferralCredit BigInt amounts, ReferralCreditUsage.restoredAmount
3. Credit application at checkout = PaymentLeg.REFERRAL_CREDIT — depends on payments Payments: enable Razorpay checkout for 1:1 consultations behind FeatureFlags.payments #113
4. Flip FeatureFlags.referrals

Related: #52, #113