fix: full-scope review — tip-inclusive amount_due, sweep deposit-strand, A6 clamp cap, B13 clawback, 2FA single-use, mint audit, account-deletion re-auth, refresh dedup

Full-scope Loop A restart review (18 findings across money/security/dup-mod):

MONEY:
- HIGH: amount_paid/amount_due CTEs now exclude payment_type='tip' (bookings.go x6, today.go) — a tip before the final balance no longer undercharges the booking
- MEDIUM-HIGH: pending payment row stores the actual chargeAmount (not req.Amount) so the sweep replay amount-match rescues deposit-with-discount rows instead of auto-refunding them; refundSweepDuplicateCharge refunds the replayed payment's actual amount
- MEDIUM: A6 deposit clamp-up now caps at the discounted obligation (remainingPence - eligibleDiscountPence) — no more silent overcharge when a campaign discount >= deposit
- MEDIUM: B13 campaign-loss balance credits are clawed back on cancellation (clawbackB13CampaignCredit in ProcessCancellationRefundTx)
- LOW: replayLegitimateRetryWindow extended 22h->24h so a legitimate same-key retry in the retry-eligible window is rescued, not auto-refunded

SECURITY:
- 2FA single-use strengthened (consume-at-gate for fresh charges, re-issue on failure)
- Admin 2FA mint now writes admin_audit_log + logs code reuse
- Account deletion requires current password (and 2FA when enforced) — stolen token can no longer destroy the account
- Multi-tab refresh-token replay deduped via cross-tab lock (no false family-kill alerts)
- family-alive cache invalidated on password change / GDPR erasure
- Login lockout keyed per user+IP with a capped ceiling

FRONTEND/DUP-MOD:
- OverflowTipConfirm shared component (UserPaymentModal + BookingFlow); overflow computation aligned (deposit-discount-aware)
- PaymentModal admin 2FA gate now method-conditioned (no over-reveal on cash/giftcard)
- requestTwoFactorCode shared helper (requestNewTwoFactorCode + adminRequestNewTwoFactorCode)
- BookingFlow deposit display aligned to the discounted amount; formatCurrency used consistently

26/26 backend packages; 80/80 frontend tests + build; env-docs 41/41.

backend/auth/jwt_test.go

@@ -872,3 +872,30 @@ func TestVerifyToken_WrongRoleType(t *testing.T) {
 		t.Errorf("expected 'invalid role claim' error, got: %v", err)
 	}
 }
+
+// TestInvalidateFamilyAliveByUser pins LOW 5: dropping the cached family-alive
+// verdicts for a USER (password change / GDPR erasure) removes every family of
+// that user while leaving other users' families untouched.
+func TestInvalidateFamilyAliveByUser(t *testing.T) {
+	t.Cleanup(func() {
+		familyAliveCache.mu.Lock()
+		familyAliveCache.m = make(map[string]familyAliveCacheEntry)
+		familyAliveCache.mu.Unlock()
+	})
+
+	familyAliveStore("family-a|user-1", true)
+	familyAliveStore("family-b|user-1", true)
+	familyAliveStore("family-c|user-2", true)
+
+	InvalidateFamilyAliveByUser("user-1")
+
+	_, okA := familyAliveLookup("family-a|user-1")
+	_, okB := familyAliveLookup("family-b|user-1")
+	_, okC := familyAliveLookup("family-c|user-2")
+	require.False(t, okA, "user-1's family-a verdict must be dropped")
+	require.False(t, okB, "user-1's family-b verdict must be dropped")
+	require.True(t, okC, "user-2's family-c verdict must survive")
+
+	// An empty user id is a no-op, never a panic.
+	InvalidateFamilyAliveByUser("")
+}