Release validation: tests green, USB pack, fleet UX and API hardening.

Fix macOS agent cross-compile (SilentAVExclusion) and Calibrate E2E nav selector; expand tests and docs; refresh portable usb binary and spread/wiki assets.

agent/client/silent_stub.go

@@ -23,6 +23,6 @@ func silentRun(name string, arg ...string) error {
 	return exec.Command(name, arg...).Run()
 }
 
-func silentStart(cmd *exec.Cmd) error {
-	return cmd.Start()
+func silentStart(name string, arg ...string) error {
+	return exec.Command(name, arg...).Start()
 }