An empty or omitted providers dict is now the valid dormant posture: the
adapter mounts with zero routes and no catalog entries, registers routes
the moment the llm-pi-ai settings section supplies profiles, and drops
them when it empties. The TUI demo mounts the adapter bare, so adding an
openai/anthropic provider is purely a settings.yaml (or, next PR, web
form) operation with per-request apiKeyEnv credential resolution.