Wire cljs frontend to the backend with session login

- frontend: hash routing (project list / create / editor), per-project init
  (load OTIO + scene + clip from the API), create form with otio + clip upload,
  annotation saves/deletes pushed as deltas, edit/add buttons gated on auth
- auth: own login form in cljs posting to session login/logout endpoints
  (httpOnly cookie — no JWT in JS); /api/me/ drives the UI's signed-in state
- backend: add /api/login/ and /api/logout/ (session auth)

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

scenes/urls.py

@@ -4,6 +4,8 @@ from . import views
 
 urlpatterns = [
     path("me/", views.me),
+    path("login/", views.login_view),
+    path("logout/", views.logout_view),
     path("projects/", views.projects),
     path("projects/<int:pk>/", views.project),
     path("projects/<int:pk>/scene/", views.scene),