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/si/input/include/qmp.h

@@ -0,0 +1,14 @@
+#ifndef VMCTL_QMP_H
+#define VMCTL_QMP_H
+#include <stddef.h>
+
+/* qmp.h — minimal QMP client over an AF_UNIX socket: connect (with capability
+ * negotiation), disconnect, and synchronous command execution. */
+
+typedef struct qmp_conn qmp_conn;
+
+qmp_conn* qmp_connect(const char* sock_path);   /* connect + qmp_capabilities; NULL on error */
+void      qmp_disconnect(qmp_conn* c);
+int       qmp_exec(qmp_conn* c, const char* cmd, char* resp, size_t cap); /* 0=return, -1=error */
+
+#endif /* VMCTL_QMP_H */