Monaco binds `KeyMod.CtrlCmd` to Cmd on macOS and Ctrl everywhere else, so the two keyboard chords in playground-format.browser.test.tsx only ever worked on one platform. Both tests passed on CI's Linux runner and failed on a Mac: the undo never fired in the first test, and the save shortcut never reached the format action in the second. Resolve the modifier the way Monaco does and use it for both chords. The keybinding itself was already correct, so no product code changes. Closes #472