fix: resolve SSE realtime ERR_INCOMPLETE_CHUNKED_ENCODING error

Add dedicated nginx location block for /api/realtime with:
- proxy_buffering off to prevent response buffering
- gzip off to avoid chunked encoding issues
- proxy_read_timeout 86400s for long-lived SSE connections
- Connection '' instead of 'upgrade' for SSE protocol

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/nginx.conf

@@ -15,6 +15,21 @@ server {
         add_header Expires "0";
     }
 
+    # SSE realtime 连接（必须在 /api/ 之前）
+    location /api/realtime {
+        proxy_pass http://192.168.1.14:8090;
+        proxy_http_version 1.1;
+        proxy_set_header Connection '';
+        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_buffering off;
+        proxy_cache off;
+        proxy_read_timeout 86400s;
+        gzip off;
+    }
+
     # API 代理到局域网 PocketBase
     location /api/ {
         proxy_pass http://192.168.1.14:8090;