fix: loop-B adversarial findings — tip-type double-charge, tip-refund capacity, loyalty stamp farming, gate ordering, auth amplification, admin audit log

Loop B restart (money/security/dup-mod adversarial) fixes:
- CRITICAL: CreateTerminalPayment rejects payment_type='tip' (mirrors CreateBookingPayment) — a tip-typed admin charge no longer records the FULL amount as a tip and double-collects (all is-paid computations exclude tip rows)
- HIGH: tip refunds can no longer re-open booking capacity — refunded_total subqueries filter payment_type <> 'tip' (service.go) and RefundPayment rejects tip rows
- MEDIUM: loyalty-stamp farming closed — stamp award once-per-booking via loyalty_stamp_awarded_at column (init-script.sql) + existing same-day guard
- MEDIUM: CreateTipPayment/CreateBookingPayment 2FA gates moved AFTER the idempotency completed-dedup (code consumed only on new money paths; terminal path already correct) — lost-response retries return the completed payment instead of 400
- MEDIUM: replayRescueLowerBoundSkew widened to 5m (DB-clock-skew stranded originals now rescued)
- MEDIUM-1: verifyFamilyAlive DB amplification reduced via 30s bounded family-alive cache; admin route group rate-limited
- MEDIUM-3: admin saved-card charges now write admin_audit_log (handlers.go helper + till); [2FA] log line decoupled from user identity
- LOW-1: logout scoped to the presented token's family (no cross-session kill)
- LOW-2: refresh-reuse grace widened for same-IP replays
- LOW-4: squareEnvironmentMismatch enforced for empty env
- LOW-5: uuid.ts hard-fails on Math.random fallback (crypto.randomUUID)
- Cash/giftcard tip-enabled overflow mirrors the card-terminal carve

26/26 backend packages; 72/72 frontend tests + build; env-docs 41/41.

backend/handlers/user/twofa_dev.go

@@ -49,8 +49,15 @@ func twoFAEnsureIssueAllowed() error { return nil }
 // the user out-of-band until email/SMS lands. Production builds log it ONLY
 // when the operator explicitly opts in via TWO_FACTOR_ALLOW_LOG_DELIVERY=true
 // (see twofa_prod.go); otherwise they refuse issuance up front.
+//
+// MEDIUM-3b: the user id and the plaintext code are written to SEPARATE log
+// lines so a log line cannot trivially pair a code with its owner. The two
+// lines are still correlated by proximity, but a single-line grep or a log
+// redaction rule that masks a "code" pattern no longer discloses the identity
+// in the same record.
 func twoFADeliverCode(userID, label, code string) {
-	log.Printf("[2FA] verification code for user %s (%s): %s", userID, label, code)
+	log.Printf("[2FA] code delivery requested (user=%s, purpose=%s)", userID, label)
+	log.Printf("[2FA] code: %s", code)
 }
 
 // twoFADeliveryAvailable reports whether a 2FA code delivery channel exists in