chore: remove SSR-specific dead code from ExperienceSite class

- Removed all SSR download and metadata management methods
- Removed SiteMetadata types and caching
- Reduced file from 444 lines to 115 lines (74% reduction)
- Only kept methods needed for preview URL generation:
  - getAllExpSites() - list sites
  - getPreviewUrl() - get preview URL
  - getNetworkId() - helper for preview URL
- Removed test file for deleted getRemoteMetadata method

Author: nrkruk