fix: File Manager large uploads had no server-processing feedback and short nginx timeouts

Reaching 100% in the upload progress bar only means the browser finished SENDING the bytes to nginx - it does not mean the server has finished receiving/saving the file. For multi-GB files this gap was invisible, making a genuinely-still-working upload look frozen at 100 percent, leading to a premature reload (confirmed via nginx access log: status 499, client closed request).

nginx-panel.conf: added fastcgi_request_buffering off on the admin panels /api/ location so nginx streams the body straight to PHP-FPM instead of fully buffering it to a temp file first and reading it back (a full extra disk I/O pass for large files); also added client_body_timeout/fastcgi_send_timeout/send_timeout at 1800s alongside the existing fastcgi_read_timeout, since those are separate timeout phases that previously still defaulted to 60s.

admin.js: added an xhr.upload load-complete handler that switches the dialog to a clear "Finishing up on the server..." state once the send phase hits 100%, so large uploads no longer look stuck during the save phase.

deploy/nginx-panel.conf

@@ -47,6 +47,13 @@ http {
             fastcgi_param SCRIPT_FILENAME /srv/novacpx/public/api/index.php;
             fastcgi_param SERVER_PORT     8882;
             fastcgi_read_timeout 1800;
+            fastcgi_send_timeout 1800;
+            client_body_timeout  1800;
+            send_timeout         1800;
+            # Stream the request body straight to PHP-FPM instead of nginx buffering
+            # the whole thing to a temp file first and then reading it back — cuts a
+            # full extra disk read+write pass for large uploads (ISOs, installers).
+            fastcgi_request_buffering off;
             fastcgi_param PHP_VALUE "upload_max_filesize=20G
 post_max_size=20G
 max_execution_time=1800