QuesaDeviceDB — LaunchAgent entry point.
Hosts the Quesa device database (Q3DdbXPC) as a persistent per-user LaunchAgent. Registers the Mach service name "com.quesa.devicedb" with launchd so that driver processes and client applications can connect by name via NSXPCConnection.
launchd on-demand activation: the agent is started automatically the first time any process opens a connection to "com.quesa.devicedb", and is restarted by launchd if it crashes (KeepAlive: {SuccessfulExit: false} in the plist).