fix(selfhost): persist local uploads for docker deployment (#1061)

* fix(selfhost): persist local uploads and proxy file routes

* fix(selfhost): keep local uploads across container recreation

* docs(selfhost): restore relative local upload dir example

docker-compose.selfhost.yml

@@ -36,6 +36,8 @@ services:
         condition: service_healthy
     ports:
       - "${PORT:-8080}:8080"
+    volumes:
+      - backend_uploads:/app/data/uploads
     environment:
       DATABASE_URL: postgres://${POSTGRES_USER:-multica}:${POSTGRES_PASSWORD:-multica}@postgres:5432/${POSTGRES_DB:-multica}?sslmode=disable
       PORT: "8080"
@@ -72,3 +74,4 @@ services:
 
 volumes:
   pgdata:
+  backend_uploads: