Expose command and button actions to the agent

[cgasgarth]

Goal

Teach the agent catalog/executor to expose one-shot command-style actions, not just scalar/enum/bool parameter widgets.

Current limitation

Buttons and other command-like actions are skipped because the catalog only maps param-backed widgets to set-float, set-choice, or set-bool.

Examples

• iop/agx/exposure range/auto tune levels
• iop/agx/exposure range/read exposure
• iop/channelmixerrgb/calibrate/accept
• iop/channelmixerrgb/calibrate/recompute
• iop/channelmixerrgb/calibrate/validate

Starting point

• darktable/src/common/agent_catalog.c:259
• darktable/src/common/agent_execute.c:481

Notes

• This likely needs a new operation kind for command/invoke actions.
• Add clear safety/validation rules so commands remain deterministic enough for agent use.