Project create/list API, clip uploads, CORS, public read

- Project gains a clip FileField; POST /api/projects/ creates one from an
  uploaded otio + clip (<=100 MB), owned by the requester
- add /api/me/ and project-detail; scene GET is public (view without login),
  PUT stays owner/collaborator-only
- serve media in DEBUG (range requests for video seek); CORS for the cljs dev
  origin with credentials
- seed_demo now builds the Challengers project from the bundled otio + 480p clip

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

scenes/admin.py

@@ -10,6 +10,8 @@ class ProjectAdmin(admin.ModelAdmin):
     search_fields = ("name",)
     filter_horizontal = ("collaborators",)
     readonly_fields = ("created", "updated")
+    fields = ("name", "owner", "collaborators", "otio", "clip", "fps", "scene",
+              "created", "updated")
 
 
 @admin.register(Revision)