vmsig: management daemon, runtime endpoint lifecycle, roster, discovery, in-tree drivers, packaging

- core: runtime attach/detach of a per-endpoint adapter trio (runtime-safe add_adapter + vmsig_core_detach_endpoint, deferred reap)
- roster: VMSIG_EV_ROSTER + CAP_ROSTER, retained per-endpoint and replayed to late subscribers
- discovery: inotify trigger dir, vmid/endpoint slot allocator, host probe; vmsigd daemon with config + per-uid admission
- input driver and vgpu perception built in-tree; vgpu perception as a separate library
- memctx: own the supplied ro_fd (closed at detach)
- deb packaging: install rules, systemd unit, tmpfiles, default config

src/adapter/input/include/input.h

@@ -1,10 +1,10 @@
 #ifndef VMSIG_INPUT_H
 #define VMSIG_INPUT_H
 
-/* Private config of the input adapter (vmctl). cfg==NULL => stub mode. Armed mode
- * (VMSIG_WITH_VMCTL) opens vmctl_open() and actuates for real. Injection is ALWAYS
- * uinput (orphaned host uinput + external QEMU input-linux). qmp_path is kept for the
- * SERVICE path (power/lifecycle via vmctl QMP), not for input injection. */
+/* Private config of the input adapter (vmctl, in-tree at src/si/input/). cfg==NULL or
+ * stub!=0 => stub mode (ack without actuation). stub==0 opens vmctl_open() and actuates for
+ * real. Injection is ALWAYS uinput (orphaned host uinput + external QEMU input-linux);
+ * qmp_path is kept for the SERVICE path (power/lifecycle via vmctl QMP), not for injection. */
 typedef struct {
     int         stub;
     const char* qmp_path;     /* for power/lifecycle (vmctl QMP); NOT input injection */