docs: Add Nginx reverse proxy configuration guide

- Added comprehensive Nginx Proxy Manager setup instructions
- Documented HTTPS to HTTP routing requirements
- Included common proxy issues and troubleshooting
- Added standard Nginx configuration examples
- Clarified SSL termination at proxy level

README.md

@@ -307,6 +307,91 @@ The URL shortener feature uses the `APP_DOMAIN` environment variable to generate
 
 Short URLs will be available at: `https://[your-domain]/s/[short-code]`
 
+## 🌐 Reverse Proxy Configuration (Nginx)
+
+When deploying behind a reverse proxy like Nginx Proxy Manager or standard Nginx, configure the proxy to route **HTTPS traffic to HTTP backend**:
+
+### ⚠️ Important Proxy Configuration
+
+- **Frontend (Public)**: HTTPS (Port 443)
+- **Backend (Docker)**: HTTP (Port 8066)
+- **SSL Termination**: At the proxy level
+
+### Nginx Proxy Manager Setup
+
+1. **Create Proxy Host**:
+   - Domain: `qr.moto-adv.com` (your domain)
+   - Forward Hostname/IP: `your-server-ip`
+   - Forward Port: `8066`
+   - **Protocol**: HTTP (not HTTPS)
+
+2. **SSL Configuration**:
+   - Enable SSL certificate (Let's Encrypt)
+   - Force SSL: Yes
+   - HTTP/2 Support: Yes
+
+3. **Advanced Settings** (if needed):
+   ```nginx
+   # Custom Nginx configuration
+   proxy_set_header Host $host;
+   proxy_set_header X-Real-IP $remote_addr;
+   proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+   proxy_set_header X-Forwarded-Proto $scheme;
+   ```
+
+### Standard Nginx Configuration
+
+```nginx
+server {
+    listen 443 ssl http2;
+    server_name qr.moto-adv.com;
+
+    # SSL Configuration
+    ssl_certificate /path/to/ssl/cert.pem;
+    ssl_certificate_key /path/to/ssl/private.key;
+
+    # Proxy to Docker container
+    location / {
+        proxy_pass http://localhost:8066;  # Note: HTTP, not HTTPS
+        proxy_set_header Host $host;
+        proxy_set_header X-Real-IP $remote_addr;
+        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+        proxy_set_header X-Forwarded-Proto $scheme;
+        proxy_set_header X-Forwarded-Host $host;
+        proxy_set_header X-Forwarded-Port $server_port;
+    }
+}
+
+# Redirect HTTP to HTTPS
+server {
+    listen 80;
+    server_name qr.moto-adv.com;
+    return 301 https://$server_name$request_uri;
+}
+```
+
+### Common Proxy Issues & Solutions
+
+| Issue | Cause | Solution |
+|-------|-------|----------|
+| 502 Bad Gateway | HTTPS→HTTPS routing | Change backend to HTTP |
+| SSL errors | Missing certificates | Configure SSL at proxy level |
+| 404 on subpaths | Missing headers | Add proxy headers |
+| Session issues | Domain mismatch | Set correct `APP_DOMAIN` |
+
+### Docker Configuration for Proxy
+
+Ensure your `docker-compose.yml` exposes the correct port:
+
+```yaml
+services:
+  qr-manager:
+    ports:
+      - "8066:5000"  # Maps container port 5000 to host port 8066
+    environment:
+      - APP_DOMAIN=qr.moto-adv.com  # Your public domain
+```
+
 ## 📱 Usage
 
 ### Generating QR Codes