feat(booth): disable card tender until a P2PE POS is on-site (cash-only)

No card processor / POS terminal on any site yet. Offering "Card" would let an
operator record a card payment that never cleared a terminal, corrupting the
till reconciliation — a fraud/error surface on an operator-adversary system.

Add apps/web/src/lib/features.ts → CARD_PAYMENTS_ENABLED=false, gating both
tender pickers (BoothPayModal, SubscriptionManager). With card off there's
nothing to choose, so the tender row is suppressed and payment defaults to
cash. UI-only gate: the Tender type, payment events, shift accounting, and
reports still understand `card`, so historical card events and a future
re-enable stay coherent.

Verified via Playwright: an unpaid-ticket modal shows Total + "Pay + open
barrier" with no tender/cash/card row.

Wiki: new concepts/card-payments.md records the current cash-only state, the
PCI-scope-out-of-app constraint, the future-POS device requirements, and the
re-enable path (flip the flag once a bank-certified P2PE terminal is
provisioned). Linked from index, parking-session, open-questions #3.

Claude-Session: https://claude.ai/code/session_01Xcm6ikLgGoCxxHrxtjkk5V

apps/web/src/SubscriptionManager.tsx

@@ -25,6 +25,7 @@ import {
   type SubscriptionPlan,
   type SubscriptionQuote,
 } from "./api.js";
+import { CARD_PAYMENTS_ENABLED } from "./lib/features.js";
 import { Modal } from "./ui/Modal.js";
 
 // Subscription admin. Create/edit/revoke/delete subscriptions + their credentials
@@ -537,7 +538,11 @@ export function SubscriptionManager({ user }: { user: SessionUser | null }) {
             )}
             {/* Tender — only relevant when selling a plan (a SALE). The sale appends a
                 signed payment so the money shows in the feed/drawer/Z-report. */}
-            {form.planId.trim() !== "" && editing === "new" && (
+            {/* Tender picker — only meaningful when there's a choice. Card is hidden until a
+                P2PE POS terminal is on-site (CARD_PAYMENTS_ENABLED); with cash-only there's
+                nothing to pick, so the whole row is suppressed (form.tender stays "cash").
+                See lib/features.ts + wiki/concepts/card-payments.md. */}
+            {form.planId.trim() !== "" && editing === "new" && CARD_PAYMENTS_ENABLED && (
               <>
                 <label className="label">{t("subs.tender")}</label>
                 <span className="flex items-center gap-3">