The enable validation was using the legacy single-provider model which
checked settings.Provider and settings.APIKey. Users configuring Ollama
via the new multi-provider UI (setting ollama_base_url) couldn't enable
AI because settings.Provider defaulted to "anthropic" which required an
API key.
Now checks GetConfiguredProviders() first - if any provider is configured
(Anthropic, OpenAI, DeepSeek, or Ollama), AI can be enabled.
Related to #847
rcourtman
eac510bb5e