## Summary
This PR removes `image_detail_original` as a runtime experiment and
makes original image detail available whenever the selected model
supports it.
Concretely, this change:
- drops the `image_detail_original` feature flag from the feature
registry and generated config schema
- makes tool-emitted image detail depend only on
`ModelInfo.supports_image_detail_original`
- updates `view_image` and `code_mode`/`js_repl` image emission to use
that capability check directly
- removes now-redundant experiment-specific tests and instruction
coverage
- keeps backward compatibility for existing configs by silently ignoring
a stale `features.image_detail_original` entry
The net effect is that `detail: "original"` is always available on
supported models, without requiring an experiment toggle.
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