[Feature Request] Support for Claude Opus 5 model selection

**Bug Description**
les questions formulés sont des questions d'architecture / montioring / supervision.

Pourquoi le switch vers opus 4.8 est imposé?

**Environment Info**
- Platform: darwin
- Terminal: iTerm.app
- Version: 2.1.272
- Feedback ID: 9c8dcf6d-6106-4b34-9ec8-8d72aea51810

**Errors**
```json
[]
```

The report names no source file, test, or entry point. Start by confirming whether Claude Opus 5 should be selectable instead of the forced Opus 4.8 switch, then trace the CLI model-selection path and define completion as the model appearing as an available selection with coverage for that behavior.

Written by the indexing model from the issue text.