Device bridge learns to stop when its gate flips off — with two injection points nothing supplies

The device bridge's start path now subscribes to feature-gate changes in addition to egress-gate changes, and shuts down with a distinct stop reason when the feature gate flips off mid-session; the egress stop path also gained its own reason string ("egress_denied" versus "gate_off"). The gate check runs through a new k8s() function that resolves gate tengu_violin_wood (falling back to false) and treats payload, override, or disabled sources as "now off". Two new inputs, isStillEnabled and onEnabledChange, are read at the default site but nothing in the bundle currently supplies them, so they appear to be seams for tests or a host rather than active code paths yet. The same call also has the bridge announce hasUnservedChange, inFlightCalls, and whenIdle to the session.