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.

server/internal/cloudflared/launcher_stub_test.go

@@ -0,0 +1,12 @@
+//go:build !windows
+
+package cloudflared
+
+import "testing"
+
+func TestStubStartStop(t *testing.T) {
+	if err := Start("", "", "token-should-not-matter"); err != nil {
+		t.Fatalf("Start: %v", err)
+	}
+	Stop()
+}