The temperature suppression was hardcoded to only match opus-4-7. Newer
Anthropic models (opus-4-8, fable) also reject the parameter with a 400.
Normalize model_name to lowercase before matching so mixed-case configs
do not fall through. Add tests for opus-4-8 and fable across adaptive,
enabled, and no-thinking paths, plus a negative test confirming ordinary
models still send temperature.
Fixes#4333