Add WisePOS E in-person card payments (Stripe Terminal)

Server-driven Stripe Terminal integration for taking in-person card payments
against an invoice, running on the same Stripe Connect connected account used
for online payments. No native app or Terminal SDK — the WisePOS E is driven
from the web backend via Stripe's REST API.

- Domain: TerminalReader entity + status enum, PaymentMethod.CardReader,
  Company.StripeTerminalLocationId / TerminalSurchargeEnabled, DbSet + tenant
  filter + indexes, IUnitOfWork repo, migration AddTerminalReaders (additive).
- StripeConnectService: location/reader registration, list, delete, process
  payment on reader, status poll, cancel, and a test-mode simulated tap. All
  routed to the connected account like the existing online-payment methods.
- TerminalController: admin reader management + per-invoice ProcessPayment,
  PaymentStatus (poll), CancelPayment, SimulateTap (test mode only). Stores the
  PaymentIntent id on the invoice; the webhook remains the authoritative writer.
- PaymentController webhook: HandlePaymentSucceededAsync records source=terminal
  payments as CardReader (online path unchanged — no source key means no change);
  new terminal.reader.action_failed handler for declines/timeouts (notification
  only, no ledger mutation). Refund path reused unchanged.
- UI: Card Readers settings tab (register/list/deactivate + in-person surcharge
  toggle, default off with a compliance warning) and an invoice "Take Card
  Payment" modal with live status polling. External JS per project convention.
- Feature bundled with the existing online-payments entitlement (no new plan
  flag); additionally requires StripeConnectStatus == Active.
- Help: HelpKnowledgeBase + Invoices help article updated.
- Tests: TerminalController validation + surcharge-routing tests (241 pass).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/PowderCoating.Web/Views/Help/Invoices.cshtml

@@ -360,6 +360,33 @@
                 The link is unique to each invoice and does not expire as long as the invoice remains unpaid.
                 Voided invoices do not generate payment links.
             </p>
+
+            <h3 id="card-readers" class="h6 fw-semibold mt-4 mb-2">In-Person Card Payments (WisePOS&nbsp;E)</h3>
+            <p>
+                Take a card payment in person against an invoice using a Stripe Terminal
+                <strong>WisePOS&nbsp;E</strong> card reader. This is included with the same plan that allows
+                online payments and runs on the same connected Stripe account &mdash; no separate merchant setup.
+            </p>
+            <ul class="mb-3">
+                <li class="mb-2"><strong>One-time setup:</strong> go to <strong>Settings &rsaquo; Card Readers</strong>
+                    (the tab appears once Stripe is connected). On the reader, open
+                    <strong>Settings &rsaquo; Generate registration code</strong> to get a three-word code, enter it
+                    with a label such as &ldquo;Front Counter,&rdquo; and click <strong>Add Reader</strong>.</li>
+                <li class="mb-2"><strong>Taking a payment:</strong> on an invoice with a balance due, click
+                    <strong>Take Card Payment</strong>, choose the reader, confirm the amount, and click
+                    <strong>Send to Reader</strong>. The reader prompts the customer to tap, insert, or swipe; the
+                    screen shows live progress and refreshes the invoice once the payment is approved.</li>
+                <li class="mb-2">The payment is recorded automatically with the method <strong>Card Reader</strong>,
+                    posts to your books, and advances the invoice to Paid or Partially Paid. Partial payments are supported.</li>
+            </ul>
+            <div class="alert alert-permanent alert-warning d-flex gap-2 mb-0" role="alert">
+                <i class="bi bi-exclamation-triangle flex-shrink-0 mt-1"></i>
+                <div>
+                    <strong>In-person surcharging is off by default.</strong> It can be enabled on the Card Readers tab,
+                    but in-person card surcharging is regulated differently than online payments and is prohibited in some
+                    states &mdash; only turn it on after confirming the rules where you operate.
+                </div>
+            </div>
         </section>
 
         <section id="payment-reminders" class="mb-5">
@@ -415,6 +442,7 @@
                     <a class="nav-link py-1 px-3 small text-body" href="#deposits">Deposits</a>
                     <a class="nav-link py-1 px-3 small text-body" href="#gift-certificates">Gift Certificates</a>
                     <a class="nav-link py-1 px-3 small text-body" href="#online-payments">Online Payments</a>
+                    <a class="nav-link py-1 px-3 small text-body" href="#card-readers">In-Person Card Payments</a>
                     <a class="nav-link py-1 px-3 small text-body" href="#payment-reminders">Payment Reminders</a>
                 </nav>
             </div>