Check if modal elements exist before adding event listeners to prevent
Uncaught TypeError: Cannot read properties of null (reading 'addEventListener')

- Welcome modal now appears correctly after login (only once per session)
- Footer links (privacy, terms, contact) appear on ALL dashboard pages
- Works for both aisbf.cloud and Tor onion service
- Fixes session flag handling so modal only gets marked seen when user actually closes it

- Add warn parameter to Config.get_provider to suppress warnings when needed
- Update analytics._get_provider_pricing to use warn=False
- Update analytics.get_model_performance to use warn=False

When visiting the analytics page, no WARNING logs are generated anymore
for user-specific providers that exist in the database but not in the
global configuration.

Fix model naming conventions: remove user- prefix from rotation/autoselect model IDs, fetch live provider models