feat(config): support large uploads with read header timeout

Disable default read and write timeouts (set to 0s) to prevent Go from
prematurely closing connections during large multi-GB uploads.

Introduce `WARPBOX_READ_HEADER_TIMEOUT` (defaulting to 15s) to protect
against slowloris-style attacks while still allowing long-running
uploads to complete. Update documentation and example configurations
accordingly.

README.md

@@ -38,6 +38,11 @@ Upload policy defaults are also configured in megabytes and can later be changed
 Runtime data is configured with `WARPBOX_DATA_DIR` and defaults to `./data` in the dev environment.
 The dev script resolves that path from the repository root.
 
+Large uploads are expected to take minutes on normal home/server connections. Keep
+`WARPBOX_READ_TIMEOUT=0s` and `WARPBOX_WRITE_TIMEOUT=0s` so Go does not close the connection
+mid-upload; `WARPBOX_READ_HEADER_TIMEOUT=15s` still protects header reads from slowloris-style
+connections.
+
 Background jobs are enabled with `WARPBOX_JOBS_ENABLED=true`. Individual jobs can be toggled with
 `WARPBOX_CLEANUP_ENABLED` and `WARPBOX_THUMBNAIL_ENABLED`, and their schedules are configured with
 `WARPBOX_CLEANUP_EVERY` and `WARPBOX_THUMBNAIL_EVERY`.
@@ -106,6 +111,9 @@ WARPBOX_DATA_DIR=/var/lib/warpbox
 WARPBOX_STATIC_DIR=/opt/warpbox-dev/backend/static
 WARPBOX_TEMPLATE_DIR=/opt/warpbox-dev/backend/templates
 WARPBOX_TRUSTED_PROXIES=127.0.0.1,::1
+WARPBOX_READ_HEADER_TIMEOUT=15s
+WARPBOX_READ_TIMEOUT=0s
+WARPBOX_WRITE_TIMEOUT=0s
 ```
 
 Example `/etc/systemd/system/warpbox.service`: