feat: stream PDF import progress via SSE with global progress bar

Replace the synchronous PDF import with Server-Sent Events streaming
between the backend (LLM) and the browser. The user can now close the
import modal and continue working while the conversion runs — a fixed
progress bar in the Layout shows real-time stage and percentage.

frontend/nginx.conf

@@ -3,6 +3,22 @@ server {
     root /usr/share/nginx/html;
     index index.html;
 
+    # Import endpoint — SSE streaming, long timeout, no buffering
+    location /api/import {
+        proxy_pass http://family-budget-backend:3000;
+        proxy_http_version 1.1;
+        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_cookie_path / /;
+        proxy_connect_timeout 5s;
+        proxy_read_timeout 600s;
+        proxy_buffering off;
+        chunked_transfer_encoding off;
+        client_max_body_size 15m;
+    }
+
     # API — проксируем на backend (сервис из docker-compose)
     location /api {
         proxy_pass http://family-budget-backend:3000;