raise upload size cap to ~1.86 GB and nginx timeouts to 1200s

Raise RequestSizeLimit/MultipartBodyLengthLimit on upload+replace-audio,
MaxUploadBytes in BatchUpload/BatchEdit, and DefaultResponseTimeoutSeconds to
1200s. Add client_max_body_size 2000m and proxy_read/send_timeout 1200s to the
nginx manager/public confs.

deploy/nginx/deepdrft-manager.conf

@@ -3,6 +3,10 @@ server {
     listen [::]:80;
     server_name __DOMAIN_APP__;
 
+    # Allow audio file uploads up to ~1.86 GB (matches the per-request ceiling on api/track/upload
+    # and api/track/{id}/replace-audio). nginx default is 1 MB, which would 413 any large upload.
+    client_max_body_size 2000m;
+
     location / {
         proxy_pass         http://localhost:__PORT_MANAGER__;
         proxy_http_version 1.1;
@@ -15,5 +19,12 @@ server {
         # WebSocket support (Blazor InteractiveServer SignalR circuits)
         proxy_set_header Upgrade    $http_upgrade;
         proxy_set_header Connection $http_connection;
+
+        # Large audio uploads stream over the SignalR WebSocket circuit for several minutes.
+        # nginx's 60 s default would drop the connection mid-transfer and silently kill the
+        # Blazor circuit — the app never sees an error, so nothing is logged. 1200 s matches
+        # the Upload:ResponseTimeoutSeconds budget already configured in the application.
+        proxy_read_timeout 1200s;
+        proxy_send_timeout 1200s;
     }
 }

deploy/nginx/deepdrft-public.conf

@@ -15,5 +15,11 @@ server {
         # WebSocket support (Blazor Server SignalR circuits + WASM interop)
         proxy_set_header Upgrade    $http_upgrade;
         proxy_set_header Connection $http_connection;
+
+        # Blazor Server SignalR circuits can be long-lived. Raise timeouts above the 60 s
+        # nginx default so idle-but-active circuits (e.g. during audio streaming) are not
+        # silently dropped.
+        proxy_read_timeout 1200s;
+        proxy_send_timeout 1200s;
     }
 }