Fix navbar/discount/invoice bugs from manual QA, add VAT breakdown, shipping-address override, checkout persistence, redesigned mobile menu

Bug fixes:
- Navbar login/logout state now updates immediately (custom ep-auth-changed
  event) instead of requiring a hard reload
- Status-change email links were broken by an un-encoded "#" in the order
  number; fixed for all 4 status emails
- Cart discount code: manual input field restored (was removed entirely)
- Quote-label underline now scales with the label's actual text width
- Number Ranges admin list now shows the invoice prefix/counter columns

Pricing & VAT:
- Prices show the real per-product VAT rate ("inkl. X% MwSt.") instead of
  a generic disclosure
- Cart/checkout/confirmation totals show the actual € amount of VAT
  included, broken down per rate when a cart spans more than one
  (new lib/taxBreakdown.ts, shared with the invoice PDF's own math)
- Account order pages gained product thumbnails and the same VAT breakdown

Low-stock warning: a "Nur noch wenige verfügbar" badge/hint across the
shop grid, spotlight, and add-to-cart variant pickers, driven by the
existing lowStockThreshold field (still never exposes raw stock counts).

Invoice PDFs: product thumbnails on every line item, a plain "Netto"
label (rate was redundant, already stated on the MwSt. line below), no
more duplicate USt-IdNr. in the header, and — for a Stornorechnung
specifically — an explicit "Versand" line that was previously only
folded silently into the tax totals.

Checkout:
- Optional deviating shipping address (separate from the billing address
  used for the invoice), with its own toggle + address form
- Full checkout draft persistence (name/address/shipping/payment
  selections) survives navigating away and back, via localStorage
- Invoice PDF shows a third "Lieferadresse" block when the shipping
  address differs from billing

Mobile navigation: fullscreen panel with a circular reveal animation from
the hamburger's corner, replacing the old in-flow accordion drawer; no
login CTA inside it (redundant with the always-visible header icon).

Admin-facing (Payload backend, mirrored where the frontend has a ported
copy of the same renderer): dashboard rebuilt as individual cards, split
into 3 task queues (received/processing/returns) instead of 2, revenue
and order counts now exclude cancelled/returned orders immediately, and
the low-stock alert links to the specific affected product(s) instead of
the unfiltered list. A new immediate email notifies the shop owner the
moment an order comes in, instead of only via the daily digest.

Testimonials admin list now groups by page instead of interleaving all
three grids' entries. ~45 English admin field descriptions translated to
German for consistency.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/api/account/orders/[orderNumber]/correction-invoice/route.ts

@@ -1,6 +1,7 @@
 import { NextResponse } from "next/server";
 import { getSessionCustomer, getCustomerOrderDetail } from "../../../../../lib/customerAuth";
 import { generateCorrectionInvoicePdf, getSellerForInvoice } from "../../../../../lib/invoiceData";
+import { getProductImagesByIds } from "../../../../../lib/payload";
 
 // On-demand download for "Stornorechnung/Gutschrift herunterladen" on
 // /konto/bestellungen/[orderNumber]. The real document was generated once
@@ -22,6 +23,7 @@ export async function GET(request: Request, { params }: { params: Promise<{ orde
   const kind = order.status === "returned" ? "gutschrift" : "storno";
 
   const seller = await getSellerForInvoice();
+  const imagesByProductId = await getProductImagesByIds(order.items.map((item) => item.product));
   const pdf = await generateCorrectionInvoicePdf(
     kind,
     {
@@ -39,7 +41,7 @@ export async function GET(request: Request, { params }: { params: Promise<{ orde
       zip: order.zip,
       city: order.city,
       country: order.country,
-      items: order.items,
+      items: order.items.map((item) => ({ ...item, imageUrl: imagesByProductId.get(item.product) ?? null })),
       subtotal: order.subtotal,
       shippingCost: order.shippingCost,
       discountAmount: order.discountAmount,

app/api/account/orders/[orderNumber]/invoice/route.ts

@@ -1,6 +1,7 @@
 import { NextResponse } from "next/server";
 import { getSessionCustomer, getCustomerOrderDetail } from "../../../../../lib/customerAuth";
 import { generateInvoicePdf, getSellerForInvoice } from "../../../../../lib/invoiceData";
+import { getProductImagesByIds } from "../../../../../lib/payload";
 
 // On-demand download for "Rechnung herunterladen" on
 // /konto/bestellungen/[orderNumber] — reuses the exact same render call as
@@ -19,6 +20,10 @@ export async function GET(request: Request, { params }: { params: Promise<{ orde
   }
 
   const seller = await getSellerForInvoice();
+  // On-demand re-download has no imageUrl snapshot to fall back to like
+  // the checkout-time attachment does (order.items only stores a numeric
+  // product id, see CustomerOrderItem) — resolved fresh here instead.
+  const imagesByProductId = await getProductImagesByIds(order.items.map((item) => item.product));
   const pdf = await generateInvoicePdf(
     {
       orderNumber: order.orderNumber,
@@ -33,8 +38,18 @@ export async function GET(request: Request, { params }: { params: Promise<{ orde
       zip: order.zip,
       city: order.city,
       country: order.country,
+      hasDifferentShippingAddress: order.hasDifferentShippingAddress,
+      shippingFirstName: order.shippingFirstName,
+      shippingLastName: order.shippingLastName,
+      shippingDeliveryMethod: order.shippingDeliveryMethod,
+      shippingStreet: order.shippingStreet,
+      shippingPackstationNumber: order.shippingPackstationNumber,
+      shippingPostNumber: order.shippingPostNumber,
+      shippingZip: order.shippingZip,
+      shippingCity: order.shippingCity,
+      shippingCountry: order.shippingCountry,
       paymentMethodTitle: order.paymentMethodTitle,
-      items: order.items,
+      items: order.items.map((item) => ({ ...item, imageUrl: imagesByProductId.get(item.product) ?? null })),
       subtotal: order.subtotal,
       shippingCost: order.shippingCost,
       discountAmount: order.discountAmount,