docs: correct the claims that no longer match the code

- the custom model option does not exist for every provider; name any model ID instead
- alpha is measured against the regional benchmark, not always SPY
- the environment overrides a fixed set of config keys
- list the providers the picker offers, and the macro data key
- drop the example call to a method that was removed

.env.example

@@ -33,7 +33,7 @@ NVIDIA_API_KEY=
 # Remote Ollama server. Unset uses http://localhost:11434/v1.
 #OLLAMA_BASE_URL=http://your-ollama-host:11434/v1
 
-# Override any DEFAULT_CONFIG key. In the CLI, a value set here skips its prompt.
+# Override these DEFAULT_CONFIG keys. Provider, models, language and round counts also skip their CLI prompt.
 #TRADINGAGENTS_LLM_PROVIDER=openai
 #TRADINGAGENTS_DEEP_THINK_LLM=gpt-5.6
 #TRADINGAGENTS_QUICK_THINK_LLM=gpt-5.6-luna