[client] Compare service URLs as endpoints, not as strings

Three places in one request path each had their own notion of "same
management URL": the config layer compared the parsed URLs as strings, the
privileged-change gate compared scheme + host + effective port, and the MDM
conflict check compared strings after filling in the default port. Only the
middle one was right.

A string comparison answers the wrong question. "https://api.netbird.io",
"https://api.netbird.io/" and "https://API.netbird.io:443" are one endpoint
written three ways, so a client restating its own management URL with a
trailing slash — a normal way to write it — was still read as a client asking
to be repointed, and the update-settings gate refused it. The MDM check had
the same flaw against the enforced value.

profilemanager.SameServiceURL is now the single comparison: same scheme, same
host case-insensitively as DNS names are, same effective port. The config
layer, the privileged-change gate and the MDM conflict check all defer to it,
so there is one answer to "did this URL change?" instead of three.

client/server/update_settings_gate_test.go

@@ -244,3 +244,27 @@ func TestSetConfig_RefusedRequestLeavesTheConfigFileUntouched(t *testing.T) {
 	require.NoError(t, err)
 	require.Equal(t, string(before), string(after), "the refused request rewrote the profile config")
 }
+
+// The container case that the string comparison still broke: the management URL
+// supplied through the environment is the stored one, written with a trailing
+// slash.
+func TestSetConfig_ManagementURLSpellingsPassTheGate(t *testing.T) {
+	for _, spelling := range []string{
+		"https://api.netbird.io",
+		"https://api.netbird.io/",
+		"https://api.netbird.io:443/",
+		"https://API.netbird.io:443",
+	} {
+		t.Run(spelling, func(t *testing.T) {
+			s, ctx, profName, username, _ := setupServerWithProfile(t)
+			s.updateSettingsDisabled = true
+
+			_, err := s.SetConfig(ctx, &proto.SetConfigRequest{
+				ProfileName:   profName,
+				Username:      username,
+				ManagementUrl: spelling,
+			})
+			require.NoError(t, err, "%q is the stored management URL written differently", spelling)
+		})
+	}
+}