feat(email): default template with inline logo + shop contact vars

Mirrors the layout from data/mail_template.png:
- Company name + greeting headline
- Body referencing the invoice number
- Inline logo (cid:invoice-logo) attached automatically
- Footer with mailto + website links

New template vars: {{shopEmail}}, {{shopWebsite}}.
Settings UI prefills empty fields with the defaults so users see and
can tweak them without losing the fallback.

app/services/invoice/email.server.ts

@@ -4,6 +4,13 @@ import type { ShopSettings } from "@prisma/client";
 
 import db from "../../db.server";
 import { getStrings, pickLanguage } from "./i18n";
+import {
+  DEFAULT_EMAIL_BODY_DE,
+  DEFAULT_EMAIL_BODY_EN,
+  DEFAULT_EMAIL_SUBJECT_DE,
+  DEFAULT_EMAIL_SUBJECT_EN,
+} from "./emailTemplates";
+import { STORED_LOGO_SENTINEL } from "./logoCache.constants";
 
 export interface SendInvoiceEmailArgs {
   shopDomain: string;
@@ -73,20 +80,20 @@ export async function sendInvoiceEmail(
     totalGross: totals.totalGross ?? "",
   });
 
-  const customSubject = language === "en" ? settings.emailSubjectEn : settings.emailSubjectDe;
-  const subject = customSubject
-    ? renderTemplate(customSubject, vars)
-    : `${t.invoice} ${invoice.invoiceNumber}` +
-      (settings.companyName ? ` — ${settings.companyName}` : "");
+  const customSubject =
+    (language === "en" ? settings.emailSubjectEn : settings.emailSubjectDe) ||
+    (language === "en" ? DEFAULT_EMAIL_SUBJECT_EN : DEFAULT_EMAIL_SUBJECT_DE);
+  const subject = renderTemplate(customSubject, vars);
 
-  const customBodyHtml = language === "en" ? settings.emailBodyHtmlEn : settings.emailBodyHtmlDe;
-  const body = customBodyHtml
-    ? renderHtmlBody(renderTemplate(customBodyHtml, vars))
-    : renderEmailBody({
-        settings,
-        invoiceNumber: invoice.invoiceNumber,
-        language,
-      });
+  const customBodyHtml =
+    (language === "en" ? settings.emailBodyHtmlEn : settings.emailBodyHtmlDe) ||
+    (language === "en" ? DEFAULT_EMAIL_BODY_EN : DEFAULT_EMAIL_BODY_DE);
+  const body = renderHtmlBody(renderTemplate(customBodyHtml, vars));
+
+  // If the rendered body references the inline logo, attach it.
+  const inlineLogo = body.html.includes("cid:invoice-logo")
+    ? await loadInlineLogo(args.shopDomain, settings)
+    : null;
 
   // Download the PDF (Shopify Files URLs are public CDN URLs).
   let pdfBytes: Uint8Array;
@@ -122,6 +129,16 @@ export async function sendInvoiceEmail(
           content: Buffer.from(pdfBytes),
           contentType: "application/pdf",
         },
+        ...(inlineLogo
+          ? [
+              {
+                filename: "logo",
+                content: Buffer.from(inlineLogo.bytes),
+                contentType: inlineLogo.contentType,
+                cid: "invoice-logo",
+              },
+            ]
+          : []),
       ],
     });
 
@@ -232,6 +249,8 @@ interface TemplateVars {
   dueDate: string;
   companyName: string;
   ownerName: string;
+  shopEmail: string;
+  shopWebsite: string;
 }
 
 function buildTemplateVars(args: {
@@ -251,6 +270,8 @@ function buildTemplateVars(args: {
     dueDate: dueMs ? new Date(dueMs).toLocaleDateString() : "",
     companyName: args.settings.companyName,
     ownerName: args.settings.ownerName,
+    shopEmail: args.settings.email,
+    shopWebsite: args.settings.website,
   };
 }
 
@@ -308,3 +329,28 @@ function parseTotals(json: string): InvoiceTotalsSnapshot {
     return {};
   }
 }
+
+/**
+ * Resolves the shop logo bytes for inline embedding. Returns null if no
+ * logo is configured or the lookup fails — the email is still sent, just
+ * without the inline image (the alt text remains visible).
+ */
+async function loadInlineLogo(
+  shopDomain: string,
+  settings: ShopSettings,
+): Promise<{ bytes: Uint8Array; contentType: string } | null> {
+  if (!settings.logoUrl) return null;
+  try {
+    if (settings.logoUrl === STORED_LOGO_SENTINEL) {
+      const cached = await db.logoCache.findUnique({ where: { shopDomain } });
+      if (!cached) return null;
+      return { bytes: new Uint8Array(cached.bytes), contentType: cached.contentType };
+    }
+    const res = await fetch(settings.logoUrl);
+    if (!res.ok) return null;
+    const ct = res.headers.get("content-type") ?? "image/png";
+    return { bytes: new Uint8Array(await res.arrayBuffer()), contentType: ct };
+  } catch {
+    return null;
+  }
+}