Script pane, realtime peer sync, and logout button

- Script pane: PDF tab beside annotations; "Add script annotation" arms
  highlight mode on the draft, ✓/✕ to confirm/cancel, auto-scrolls to the
  active annotation's highlights during playback. Adds Project.script.
- Realtime: Django Channels websocket per project broadcasts attributed
  scene deltas after each save; peers merge them in (keeping local drafts).
- Logout link in the editor project-bar.

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

scenes/consumers.py

@@ -0,0 +1,22 @@
+import json
+
+from channels.generic.websocket import AsyncWebsocketConsumer
+
+
+class SceneConsumer(AsyncWebsocketConsumer):
+    """One connection per open project. Joins the project's group and relays
+    scene deltas the server broadcasts (see scenes.views.scene). Read-only:
+    edits still go through the PUT endpoint, which is the broadcast source."""
+
+    async def connect(self):
+        self.pk = self.scope['url_route']['kwargs']['pk']
+        self.group = f'project_{self.pk}'
+        await self.channel_layer.group_add(self.group, self.channel_name)
+        await self.accept()
+
+    async def disconnect(self, code):
+        await self.channel_layer.group_discard(self.group, self.channel_name)
+
+    # broadcast handler: {type: "scene.delta", delta: {...}}
+    async def scene_delta(self, event):
+        await self.send(text_data=json.dumps(event['delta']))