App 2.4.2: pairing dialog shows errors instead of closing

- On a failure the pairing dialog stays open and shows the reason in
  red (Cancel becomes Close); before, it closed at once and the reason
  was only in the Server tab's status line.
- "Pairing is not enabled" only when the server says so. Any other 404
  (a server older than 2.1.0, or a proxy's page) is reported as a
  server without pairing.
- Pairing and Test connection name the problem: a server name that
  does not resolve (Test connection used to say "No internet
  connection"), a server that does not answer, or the HTTP status.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QLJfZQZeAKAwSqViTmLzki

app/src/test/java/com/evsuite/abrp/PairingClientTest.java

@@ -27,6 +27,7 @@ public class PairingClientTest {
     private String url;
     private final Deque<Integer> pollStatuses = new ArrayDeque<>();
     private volatile int startStatus = 201;
+    private volatile String startErrorBody = "{\"error\":\"pairing is not enabled\"}";
     private volatile String lastStartBody;
 
     @Before
@@ -73,7 +74,7 @@ public class PairingClientTest {
             response = status == 201
                     ? "{\"deviceCode\":\"dev-code\",\"userCode\":\"K7F-3QX\",\"verificationUri\":\"https://car.example.com/pair\","
                       + "\"verificationUriComplete\":\"https://car.example.com/pair?code=K7F-3QX\",\"expiresIn\":600,\"interval\":5}"
-                    : "{\"error\":\"pairing is not enabled\"}";
+                    : startErrorBody;
         } else {
             Integer next;
             synchronized (pollStatuses) { next = pollStatuses.poll(); }
@@ -119,6 +120,19 @@ public class PairingClientTest {
         assertEquals(PairingClient.Outcome.EXPIRED, PairingClient.poll(url, "dev-code").outcome);
     }
 
+    @Test
+    public void aServerWithoutPairingIsNotMistakenForPairingSwitchedOff() throws Exception {
+        // e.g. server 2.0.0, or a proxy's own 404 page
+        startStatus = 404;
+        startErrorBody = "404 page not found";
+        try {
+            PairingClient.start(url, "6f1a2b3c-4d5e-4f60-8a9b-0c1d2e3f4a5b");
+            fail("expected HttpStatusException");
+        } catch (PairingClient.HttpStatusException expected) {
+            assertEquals(404, expected.status);
+        }
+    }
+
     @Test
     public void pairingSwitchedOffOnTheServerIsReportedAsSuch() throws Exception {
         startStatus = 404;