fix(dev): Vite-API-Proxy, Auth, Stripe-Mails und Backend-Erweiterungen

- Client: API-Basis-URL (joinApiUrl, /v1-Falle), Vite strictPort + Proxy 127.0.0.1, Nicht-JSON-Fehler

- Server: /api-404 ohne Wildcard-Bug, SPA-Fallback, Auth-Middleware, Cron, Mailer, Crypto

- Routen: OAuth-State, Email/Stripe/Analytics; client/.env.example

Made-with: Cursor

server/middleware/errorHandler.mjs

@@ -3,6 +3,8 @@
  * Catches all errors and returns consistent JSON responses
  */
 
+import { AppwriteException } from 'node-appwrite'
+
 export class AppError extends Error {
   constructor(message, statusCode = 500, code = 'INTERNAL_ERROR') {
     super(message)
@@ -56,11 +58,28 @@ export function errorHandler(err, req, res, next) {
     stack: process.env.NODE_ENV === 'development' ? err.stack : undefined,
   })
 
-  // Default error values
-  let statusCode = err.statusCode || 500
-  let code = err.code || 'INTERNAL_ERROR'
+  // Default error values (AppwriteException uses numeric err.code — do not reuse as JSON "code" string)
+  let statusCode =
+    typeof err.statusCode === 'number' ? err.statusCode : undefined
+  let code = typeof err.code === 'string' && err.code ? err.code : 'INTERNAL_ERROR'
   let message = err.message || 'Ein Fehler ist aufgetreten'
 
+  if (
+    err instanceof AppwriteException &&
+    typeof err.code === 'number' &&
+    err.code >= 400 &&
+    err.code < 600
+  ) {
+    statusCode = err.code
+    code = err.type || 'APPWRITE_ERROR'
+    message = err.message || message
+    err.isOperational = true
+  }
+
+  if (statusCode === undefined) {
+    statusCode = 500
+  }
+
   // Handle specific error types
   if (err.name === 'ValidationError') {
     statusCode = 400