Rename AdventureLog to Voyage and add fork attribution

- Replace all AdventureLog references with Voyage across ~102 files
  (7 case variants: AdventureLog, adventurelog, Adventurelog, ADVENTURELOG,
  AdventUrelog, AdventureLOG, adventure-log, adventure_log)
- Rename brand, static, and documentation assets to use voyage naming
- Rename install_adventurelog.sh → install_voyage.sh
- Update README.md and voyage_overview.md to credit AdventureLog as
  the upstream project and Sean Morley as its original creator

backend/server/adventures/views/collection_view.py

@@ -481,7 +481,7 @@ class CollectionViewSet(viewsets.ModelViewSet):
         collection = self.get_object()
 
         export_data = {
-            'version': getattr(settings, 'ADVENTURELOG_RELEASE_VERSION', 'unknown'),
+            'version': getattr(settings, 'VOYAGE_RELEASE_VERSION', 'unknown'),
             # Omit export_date to keep template-friendly exports (no dates)
             'collection': {
                 'id': str(collection.id),