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.

package.json

@@ -9,7 +9,7 @@
     "deploy": "shopify app deploy",
     "config:use": "shopify app config use",
     "env": "shopify app env",
-    "start": "react-router-serve ./build/server/index.js",
+    "start": "node ./server.js",
     "docker-start": "npm run setup && npm run start",
     "setup": "prisma generate && prisma migrate deploy",
     "lint": "eslint --ignore-path .gitignore --cache --cache-location ./node_modules/.cache/eslint .",
@@ -17,7 +17,8 @@
     "prisma": "prisma",
     "graphql-codegen": "graphql-codegen",
     "vite": "vite",
-    "typecheck": "react-router typegen && tsc --noEmit"
+    "typecheck": "react-router typegen && tsc --noEmit",
+    "test": "tsx --test tests"
   },
   "type": "module",
   "engines": {
@@ -29,7 +30,11 @@
     "@react-router/dev": "^7.12.0",
     "@react-router/fs-routes": "^7.12.0",
     "@react-router/node": "^7.12.0",
+    "@react-router/express": "^7.14.2",
     "@react-router/serve": "^7.12.0",
+    "compression": "^1.8.1",
+    "express": "^4.22.1",
+    "morgan": "^1.10.1",
     "@shopify/app-bridge-react": "^4.2.4",
     "@shopify/shopify-app-react-router": "^1.1.0",
     "@shopify/shopify-app-session-storage-prisma": "^8.0.0",