KSCR Daemon 2.1.0

Some simplicity refactoring, handling and validation, and bug prevention:
midi_bridge: fault-safe OA reads, wrap-split payload copy, mask validation
midi_bridge, nks4_inject: hold a mutex across calls into OA
vkbd: fix unload-vs-setup ordering; add test-only setup_delay_ms
eva_mode: distinguish alloc failure from "Eva not found"
screenremote: fix SysEx tail timeout, EINTR drop, and silent failures
screenremote: factor out due() throttle and rtf5 writer; bump to 2.1.0
docs: correct RT_chord_trigger, STATE, and .boot notes