Adds an Asset Picker and upload dialog to the CASE editor so authors can
insert `:::evidence` directives that reference backend assets, and opens
projectWorkingCopy's two evidence gates so Instant Preview accepts a key
backed by a freshly loaded READY asset instead of only the one hardcoded
legacy key. The editor screen now owns the loaded Asset list so the
Picker, the upload dialog, and Instant Preview all read the same array,
and a freshly uploaded asset appears in the preview without a refetch.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
