Reviewer caught: the macOS file-URL loop returned after the first
image-shaped path, silently dropping the rest of a multi-image
selection. The bracketed-paste handler in `CustomEditor.handleInput`
already iterates every extracted image path; the keybind path now does
the same. Mixed selections (one .pdf + two images) still attach all
images and skip the non-images.
Tests cover (a) multi-image selection (3 attached), (b) mixed selection
with the file-URL fallback owning the outcome (text fallback MUST NOT
run when at least one file URL was an image).
Refs #3506
roboomp
257b515353