feat(billing): 80mm thermal invoice layout (ADD-P001)

GET billing/invoices/:id/document?format=thermal renders a dedicated 80mm
receipt template (72mm printable, 4mm margins each side), not a CSS variant
of the A4 layout — the A4 CSS is absolutely-positioned/fixed-px, tuned for a
210mm page, and doesn't reflow at thermal width. No seal (not a thermal
convention, renders badly on 1-bit thermal heads); line items stack
(description, then qty x rate = amount) instead of a table, since a real
table leaves ~10-14 chars for description at this width.

PdfRenderService gains a thermal render path: full 80mm-width viewport,
content height measured via page.evaluate after settle (continuous-roll
receipts have no fixed page length), and a noFallback option — a Chromium
failure throws a clear error instead of silently degrading to the generic
A4/no-QR fallback, which would hand back a different document than what was
asked for. The frontend surfaces that as a toast pointing at the existing A4
download.

format is strictly validated (a4|thermal only, BadRequestException
otherwise), not silently coerced.

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

apps/edr-freight-api/src/modules/billing/billing.service.spec.ts

@@ -927,6 +927,7 @@ describe("BillingService.document", () => {
 
   const build = (invoice: Record<string, unknown>) => {
     const render = jest.fn().mockResolvedValue({ filename: "x.pdf", buffer: Buffer.from("") });
+    const renderThermal = jest.fn().mockResolvedValue({ filename: "x-thermal.pdf", buffer: Buffer.from("") });
     const service = new BillingService(
       {} as never,
       { findById: jest.fn().mockResolvedValue(invoice) } as never,
@@ -934,7 +935,7 @@ describe("BillingService.document", () => {
       {} as never,
       {} as never,
       {} as never,
-      { render } as never,
+      { render, renderThermal } as never,
       {} as never,
       {
         get: (key: string) =>
@@ -943,7 +944,7 @@ describe("BillingService.document", () => {
             : undefined,
       } as never, // config
     );
-    return { service, render };
+    return { service, render, renderThermal };
   };
 
   it("adds no EIMS IRN row and no QR for an unregistered invoice", async () => {
@@ -1000,4 +1001,24 @@ describe("BillingService.document", () => {
     expect(model.summary).toContainEqual({ label: "EIMS IRN", value: "IRN-123" });
     expect(model.qrImageUrl).toBe("data:image/png;base64,signed-payload");
   });
+
+  it("calls render (not renderThermal) for the default format", async () => {
+    const { service, render, renderThermal } = build(invoiceRow());
+    jest.spyOn(service as never, "toDocumentModel").mockResolvedValue({} as never);
+
+    await service.document("inv-1");
+
+    expect(render).toHaveBeenCalledTimes(1);
+    expect(renderThermal).not.toHaveBeenCalled();
+  });
+
+  it("calls renderThermal (not render) for format 'thermal'", async () => {
+    const { service, render, renderThermal } = build(invoiceRow());
+    jest.spyOn(service as never, "toDocumentModel").mockResolvedValue({} as never);
+
+    await service.document("inv-1", "thermal");
+
+    expect(renderThermal).toHaveBeenCalledTimes(1);
+    expect(render).not.toHaveBeenCalled();
+  });
 });