fix(observability,webhooks,i18n): timestamped logs, dedupe webhook retries, default non-de locales to English

- New custom server.js (replaces react-router-serve): ISO timestamps on
  all console.* output and on access logs, and skip successful /healthz
  polls so real traffic stays visible.
- New ProcessedWebhook table + dedupe helper keyed on
  X-Shopify-Webhook-Id; stops Shopify retries from triggering a second
  invoice email when the original delivery exceeded the 5s ack timeout.
- orders/create + orders/fulfilled now respond 200 immediately and run
  the PDF/email work in the background so we stay under that timeout.
- pickLanguage(): non-German locales (it, fr, es, ...) now default to
  English instead of falling back to German. Empty/unknown still maps to
  'de' so the per-shop defaultLanguage chain keeps working.
- Tests for pickLanguage and dedupe via node --test + tsx.

server.js

@@ -0,0 +1,81 @@
+// Custom production server for the React Router build.
+//
+// Replaces `react-router-serve` so we can:
+//   - prefix every console line with an ISO timestamp,
+//   - use a richer morgan format (with timestamp + content-length),
+//   - skip access logs for successful /healthz probes (they would otherwise
+//     drown out everything useful — Docker/Caddy poll them every couple of
+//     seconds).
+//
+// Behaviour is otherwise intentionally identical to `@react-router/serve`'s
+// CLI (compression, /assets immutable cache, public/ static, SIGTERM/SIGINT
+// handling).
+
+import { createRequestHandler } from "@react-router/express";
+import compression from "compression";
+import express from "express";
+import morgan from "morgan";
+
+// ---------------------------------------------------------------------------
+// Console timestamps — patch BEFORE anything else logs.
+// ---------------------------------------------------------------------------
+const ts = () => `[${new Date().toISOString()}]`;
+for (const level of ["log", "info", "warn", "error", "debug"]) {
+  const original = console[level].bind(console);
+  console[level] = (...args) => original(ts(), ...args);
+}
+
+const PORT = Number(process.env.PORT || 3000);
+const HOST = process.env.HOST;
+
+const buildModule = await import("./build/server/index.js");
+const build = buildModule.default ?? buildModule;
+
+const app = express();
+app.disable("x-powered-by");
+app.use(compression());
+
+// Static assets emitted by the React Router build.
+app.use(
+  "/assets",
+  express.static("build/client/assets", { immutable: true, maxAge: "1y" }),
+);
+app.use(express.static("build/client", { maxAge: "1h" }));
+app.use(express.static("public", { maxAge: "1h" }));
+
+// Access log: ISO timestamp + standard request info; suppress healthy
+// /healthz polls so real traffic stays visible.
+morgan.token("isotime", () => new Date().toISOString());
+app.use(
+  morgan(
+    ":isotime :method :url :status :res[content-length] - :response-time ms",
+    {
+      skip: (req, res) => req.url === "/healthz" && res.statusCode < 400,
+    },
+  ),
+);
+
+app.all(
+  "*",
+  createRequestHandler({ build, mode: process.env.NODE_ENV }),
+);
+
+const onListen = () => {
+  console.log(
+    `[server] listening on http://${HOST ?? "localhost"}:${PORT}`,
+  );
+};
+
+const server = HOST
+  ? app.listen(PORT, HOST, onListen)
+  : app.listen(PORT, onListen);
+
+for (const signal of ["SIGTERM", "SIGINT"]) {
+  process.once(signal, () => {
+    console.log(`[server] received ${signal}, shutting down`);
+    server.close((err) => {
+      if (err) console.error("[server] close error:", err);
+      process.exit(0);
+    });
+  });
+}