Fix FOUC and improve Web UI i18n experience

- Fix Flash of Unstyled Content (FOUC) by hiding page until translations load
  - Hide body initially with visibility:hidden
  - Show content after translations are applied to avoid English flash
- Fix authenticated indicator layout with white-space:nowrap
- Add "●" symbol to translation files to prevent disappearance on reload
- Enable network access by binding server to 0.0.0.0 in test config
- Simplify test config API keys to single entry

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

server/config/test_config.yaml

@@ -1,15 +1,14 @@
 server:
-  host: "127.0.0.1"  # localhost only for testing
+  host: "0.0.0.0"  # Listen on all interfaces (accessible from local network)
   port: 8080
   log_level: "DEBUG"  # Verbose logging for testing
   cors_origins:
     - "*"
 
 auth:
-  # Test API keys - DO NOT use in production!
+  # Test API key - DO NOT use in production!
   api_keys:
     test_client: "eb8a89cfd33ab067751fd0e38f74ddf7ac3d75ff012fbab35a616c45c12e0c8d"
-    web_dashboard: "4b958666d32b368a89781da040a615283541418753d610858d6eb5411296dcb6"
 
 processing:
   default_fps: 30