Reload the browser on template and static changes in dev

Adds django-browser-reload: runserver already restarts on Python changes, but
the browser had to be refreshed by hand for every template or CSS edit. It also
watches static/, so a Tailwind rebuild now refreshes the page on its own.

Mounted only under DEBUG -- it injects a script into every HTML response and
serves an open event stream, neither of which belongs in production; a test
holds that line. Its endpoint is exempt from RequireMFAMiddleware, otherwise a
not-yet-enrolled staff user has the stream redirected away and live reload dies
on the MFA enrolment page, which is exactly a page we are restyling.

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

authentication/middleware.py

@@ -17,7 +17,9 @@ from django.urls import reverse
 from club.models import ClubRole
 
 #: Paths a not-yet-enrolled user must still reach (to enrol, or to log out).
-EXEMPT_PREFIXES = ("/accounts/", "/static/", "/media/")
+#: ``/__reload__/`` is django-browser-reload's event stream, which only exists
+#: under DEBUG — without it, live reload dies on the enrolment page itself.
+EXEMPT_PREFIXES = ("/accounts/", "/static/", "/media/", "/__reload__/")
 
 ELEVATED_ROLES = (ClubRole.Roles.ADMIN, ClubRole.Roles.EDITOR)