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_test.go

@@ -54,12 +54,8 @@ func TestSilentCmdReturnsCmd(t *testing.T) {
 	}
 }
 
-func TestSilentStartAndWait(t *testing.T) {
-	cmd := exec.Command("true")
-	if err := silentStart(cmd); err != nil {
+func TestSilentStart(t *testing.T) {
+	if err := silentStart("true"); err != nil {
 		t.Fatalf("silentStart: %v", err)
 	}
-	if err := cmd.Wait(); err != nil {
-		t.Errorf("cmd.Wait after silentStart: %v", err)
-	}
 }