feat: Implement SAM structure mirroring in PostgreSQL for study plans and courses

- Added functionality to save study plans and courses in SAM format to PostgreSQL.
- Updated SQL queries to reflect SAM-native column names and handle conflicts appropriately.
- Introduced new fields in the Asset model for English level and SAM identifiers.
- Enhanced the TestTemplateForm component to manage linked assets and shared materials.
- Created a new AdminSharedMaterialsPage for uploading ZIP files of shared materials.
- Added migrations to create SAM mirror tables and update the assets table with new columns.

nginx/studio.conf

@@ -1,22 +1,27 @@
 # Custom nginx configuration for OpenCCB Studio
 # This overrides the default location block to route API requests correctly
 
+# Allow large ZIP uploads (RAG bulk import can exceed 2GB).
+client_max_body_size 4096m;
+client_body_timeout 1800s;
+
 # API routes that need to go to port 3001
 # Prefer the explicit `/cms-api/*` prefix for frontend fetches. This avoids collisions
 # with Next.js pages like `/courses` and `/admin` that share the same host.
 location /cms-api/ {
     rewrite ^/cms-api/(.*)$ /$1 break;
     proxy_pass http://openccb-studio:3001;
+    proxy_request_buffering off;
     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 $http_x_forwarded_proto;
     proxy_set_header Connection "";
     proxy_http_version 1.1;
-    proxy_connect_timeout 60s;
-    proxy_send_timeout 600s;
-    proxy_read_timeout 600s;
-    send_timeout 600s;
+    proxy_connect_timeout 120s;
+    proxy_send_timeout 3600s;
+    proxy_read_timeout 3600s;
+    send_timeout 3600s;
 }
 
 location /lms-api/ {