fix(agent): divert a single-bound gesture button (#1569)

* fix(agent): divert a single-bound gesture button

Turning gestures off leaves the gesture button on Single(MissionControl).
The capture plan compared that against the vestigial single-action
default, left the button native, and the firmware gives it no host
action, so the press did nothing while the GUI showed Mission Control.
Gesture sources now divert for any single action except None, the same
rule the haptic panel already used.

* docs(core): drop the stale native-capture note from set_gesture_mode