Support non-darkroom controls in the agent catalog

[cgasgarth]

Goal

Allow the agent to discover and edit supported controls outside the current darkroom dev->iop walk.

Current limitation

The catalog only iterates darkroom image-operation modules.

Starting point

• darktable/src/common/agent_catalog.c:452
• darktable/src/common/agent_catalog.c:466

Notes

• Decide the first non-darkroom scope to support (for example other edit-relevant views or shared controls), rather than trying to expose everything at once.
• Keep the same descriptor model where possible so server/runtime logic does not fork unnecessarily.