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/location_image_view.py

@@ -198,7 +198,7 @@ class ContentImageViewSet(viewsets.ModelViewSet):
             return Response({"error": result}, status=status.HTTP_400_BAD_REQUEST)
 
         try:
-            headers = {'User-Agent': 'AdventureLog/1.0 (Image Proxy)'}
+            headers = {'User-Agent': 'Voyage/1.0 (Image Proxy)'}
             max_redirects = 3
             current_url = image_url