feat(invite): referral push notifications — accepted, inviter reward, invitee reward

[islandbitcoin]

What

The invite slice of ENG-531 (event notifications): three pushes across the referral flow, queued since the feature launch plan.

Recipient	Trigger	Copy
Inviter	invite redeemed (ACCEPTED transition, redeem resolver)	"Your invite was accepted 🎉 — {name} just joined Flash from your invite" (no-name fallback)
Inviter	their reward leg confirmed paid (award-referral-reward)	"Referral reward earned — US$X credited to your wallet"
Invitee	their reward leg confirmed paid	"Welcome reward received — US$X credited to your wallet"

Design

• Best-effort throughout — the senders can never throw into the redeem or payout paths (outer try/catch + logged warns; fire-and-forget call sites).
• Pending IBEX legs do NOT notify — money unconfirmed, ops reconciles first; only paid legs push.
• Mirrors the bridge-KYC push module exactly: account → user → deviceTokens, localized phrases (notification.referral.* added to en + es), dead-token pruning via removeDeviceTokens, Payments category, typed data payload (referral_accepted / referral_inviterReward / referral_inviteeReward) for client-side routing.

Tests

7 new module tests (phrase selection, $ formatting, dead-token pruning, never-throws ×2) + wiring assertions: award spec (both legs push on paid; failed leg never), redeem spec (accepted push fires with the inviter's id). Full unit suite 1396 passed. (kyc.spec's logger stub gained .child() — the new import chain reaches the push module's load-time child logger.)

No schema changes, no migrations — deployable on the next train.

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