Do not let DEBUG=True take down a container that has no dev deps

The image installs with --no-dev, so django_browser_reload is absent. Settings and
urls both assumed DEBUG implied it was installed, so DJANGO_DEBUG=True in a
deployed container did not merely turn on debugging: the app refused to start, with
a ModuleNotFoundError that says nothing about the actual mistake.

Both now guard on the module being importable. Reproduced the failure locally by
hiding the package with DEBUG on, and confirmed the urlconf loads afterwards.

DEPLOYMENT.md says the obvious thing out loud: a test server is still a deployment
-- real TLS, real domain, real passkeys -- so DEBUG stays off there. The crash is
fixed; the reason to keep it off was never the crash.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

rosterchief/urls.py

@@ -30,6 +30,11 @@ urlpatterns = [
 ]
 
 if settings.DEBUG:
-    urlpatterns += [path("__reload__/", include("django_browser_reload.urls"))]
+    # Only when the app is actually installed. It is a dev dependency, and the production
+    # image installs with --no-dev, so DEBUG=True in a container must not take the whole
+    # site down over a package that is only there to refresh a browser tab.
+    if settings.BROWSER_RELOAD_AVAILABLE:
+        urlpatterns += [path("__reload__/", include("django_browser_reload.urls"))]
+
     # Club logos are uploads: runserver has to serve MEDIA_ROOT itself.
     urlpatterns += static(settings.MEDIA_URL, document_root=settings.MEDIA_ROOT)