models: add Claude Opus 5 for Anthropic

[manojp99]

Summary

• add anthropic:claude-opus-5 to the curated native Anthropic model matrix
• expose its 1M context window and agentic vision capabilities in the GUI
• cover the model label, provider suggestion, and adaptive-thinking path

Testing

• python3 -m pytest tests/test_model_errors.py tests/test_anthropic_provider.py::test_thinking_config_is_model_family_aware -q (6 passed)
• git diff --check

Follow-up

Broader provider catalog discovery is tracked in #594.