fix: SSE blockiert gunicorn-Worker - auf gthread umstellen

Mit 4 synchronen Workern hielt jede SSE-Verbindung dauerhaft einen
ganzen Worker besetzt. 4 offene Browser-Tabs -> alle anderen
Requests blockiert -> "Dateien laden dauert ewig".

Loesung: gthread worker-class mit 2 Workern x 16 Threads = 32
gleichzeitige Slots. Lang laufende SSE-Streams belegen nur je
einen Thread, regulaere Requests laufen unbeeintraechtigt.

nginx.example.conf: separater Location-Block fuer /api/sync/events
mit proxy_buffering off und 24h Read-Timeout, damit die Events
sofort durchkommen und die Verbindung nicht abbricht.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Dockerfile

@@ -35,4 +35,9 @@ ENV UPLOAD_PATH=/app/data/files
 
 EXPOSE 5000
 
-CMD ["gunicorn", "--bind", "0.0.0.0:5000", "--workers", "4", "--timeout", "120", "wsgi:application"]
+# gthread worker class so SSE long-poll connections don't starve regular requests.
+# 2 workers x 16 threads = 32 concurrent slots; each SSE client just holds one thread.
+CMD ["gunicorn", "--bind", "0.0.0.0:5000", \
+     "--worker-class", "gthread", "--workers", "2", "--threads", "16", \
+     "--timeout", "120", "--keep-alive", "65", \
+     "wsgi:application"]

nginx.example.conf

@@ -24,6 +24,23 @@ server {
         proxy_set_header Connection "upgrade";
     }
 
+    # Server-Sent Events: Puffer aus, lange Read-Timeouts, sonst bricht die
+    # Live-Refresh-Verbindung nach ein paar Sekunden ab.
+    location /api/sync/events {
+        proxy_pass http://127.0.0.1:5000;
+        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_http_version 1.1;
+        proxy_buffering off;
+        proxy_cache off;
+        proxy_read_timeout 24h;
+        proxy_send_timeout 24h;
+        chunked_transfer_encoding on;
+    }
+
     # CalDAV/CardDAV braucht spezielle Methoden
     location /dav/ {
         proxy_pass http://127.0.0.1:5000;