feat(smith): add qwen3.8 model completion

[edwin-zvs]

Summary

• add ollama:qwen3.8 to the shared curated model catalog
• cover the Ollama picker entries in the protocol catalog test

Testing

• cargo test -p construct-protocol model_completions_are_offered_after_model_command
• cargo build
• git diff --check

Formatting

• cargo fmt --all -- --check reports pre-existing formatting drift across the repository; this patch introduces no formatter diff in its changed lines.