Groups the selected layers and clips them to a frame rect (their bounds)
via a rectangular layer mask — the visual result of Photoshop's Frame for
this command, built from existing group + mask primitives (no doc-model
change). Headless/scriptable; 2 tests. Parity 605 -> 606; FLOOR 601.
(A distinct Frame layer type + the interactive Frame tool K are a later arc.)
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>