feat(one-time-downloads): add expiry and retry configuration

Introduce new environment variables to control the behavior of one-time download boxes:
- `WARPBOX_ONE_TIME_DOWNLOAD_EXPIRY_SECONDS`: Sets the lifetime of a one-time box after uploads are complete.
- `WARPBOX_ONE_TIME_DOWNLOAD_RETRY_ON_FAILURE`: Determines whether a box remains available if the ZIP creation or transfer fails.

To support these settings, the ZIP delivery process was refactored to use a temporary file. This ensures that a one-time box is only marked as consumed after the file has been successfully transferred to the client, preventing data loss on network interruptions.

Additionally, added a `DecorateFiles` helper in the box store to reduce code duplication.

lib/config/config_test.go

@@ -38,6 +38,7 @@ func TestEnvironmentOverrides(t *testing.T) {
 	t.Setenv("WARPBOX_GLOBAL_MAX_FILE_SIZE_BYTES", "100")
 	t.Setenv("WARPBOX_BOX_POLL_INTERVAL_MS", "2000")
 	t.Setenv("WARPBOX_ADMIN_USERNAME", "root")
+	t.Setenv("WARPBOX_ONE_TIME_DOWNLOAD_RETRY_ON_FAILURE", "true")
 
 	cfg, err := Load()
 	if err != nil {
@@ -59,6 +60,9 @@ func TestEnvironmentOverrides(t *testing.T) {
 	if cfg.AdminUsername != "root" {
 		t.Fatalf("unexpected admin username: %s", cfg.AdminUsername)
 	}
+	if !cfg.OneTimeDownloadRetryOnFailure {
+		t.Fatal("expected one-time retry-on-failure env override to be applied")
+	}
 	if cfg.Source(SettingAPIEnabled) != SourceEnv {
 		t.Fatalf("expected API setting source to be env, got %s", cfg.Source(SettingAPIEnabled))
 	}
@@ -160,6 +164,7 @@ func clearConfigEnv(t *testing.T) {
 		"WARPBOX_API_ENABLED",
 		"WARPBOX_ZIP_DOWNLOADS_ENABLED",
 		"WARPBOX_ONE_TIME_DOWNLOADS_ENABLED",
+		"WARPBOX_ONE_TIME_DOWNLOAD_RETRY_ON_FAILURE",
 		"WARPBOX_RENEW_ON_ACCESS_ENABLED",
 		"WARPBOX_RENEW_ON_DOWNLOAD_ENABLED",
 		"WARPBOX_DEFAULT_GUEST_EXPIRY_SECONDS",