List usable model ids when PI_MODEL points at a provider without credentials

Claude-Session: https://claude.ai/code/session_01JtuZTCMW9TyogEmBgGf8JT

.env.example

@@ -6,6 +6,9 @@ TELEGRAM_OWNER_ID=123456789
 WORKSPACE_DIR=./workspace
 OPENAI_API_KEY=
 STT_MODEL=gpt-4o-transcribe
+# PI_MODEL: leave empty for the first model Pi has credentials for. With the Claude Code
+# subscription package use ids like pi-claude-code-provider/opus. Ids like anthropic/claude-opus-4-7
+# need an ANTHROPIC_API_KEY. Run `pi --list-models` to see every id.
 PI_MODEL=
 SECRETARY_TIMEZONE=
 SECRETARY_SHELL=