Next/back button assignment moves from a frame-level "Button assignments" card into each widget's own gear-icon dialog, prefilled with a sane default at creation (photos/calendar -> advance/back, whiteboard/weather -> check_now, others -> none). At most one binding per (widget, button) now -- cross-widget execution order never mattered since each widget's action only touches its own state. New firmware capability: holding NEXT or BACK past a configurable duration (min 3s, server-side default) triggers a frame-wide action instead of the per-widget short-press one -- cycling saved layouts, refreshing all widgets, or freezing/unfreezing every photo widget (see app/global_actions.py). Firmware next/back checks gain the same hold-duration polling the combo button already had; the threshold comes from the previous wake's /frame/config fetch (persisted in NVS), since this wake's button decision happens before that request. Not done here: firmware/version.txt is intentionally left unbumped -- this hasn't been built or hardware-tested (no ESP-IDF toolchain in this environment), so no firmware release build should be triggered yet.