vpui.set_text_mode selects:
- TEXT_MODE_DIRECT: vpui imports fonttools, loads /FONTS/FONT.TTF and
builds the 8x16 atlas in-process.
- TEXT_MODE_MANAGED (default): text is queued per frame and drawn by
Explorer through the new DESK_REQ_TEXT request; Explorer uses the same
fonttools atlas.
Remove the fixed VPUI.ATL asset and its loader.