Propagate realm-reported build to world handshake for vanilla compatibility

- Prefer realm.build over profile worldBuild when non-zero in CMSG_AUTH_SESSION
- Fixes vanilla (1.12.1 build 5875) servers rejecting connection due to wrong build
- Suppress v0.0.0 display in realm list when version info is all zeros

src/core/application.cpp

@@ -1349,16 +1349,18 @@ void Application::setupUICallbacks() {
         }
 
         uint32_t realmId = 0;
+        uint16_t realmBuild = 0;
         {
             // WotLK AUTH_SESSION includes a RealmID field; some servers reject if it's wrong/zero.
             const auto& realms = authHandler->getRealms();
             for (const auto& r : realms) {
                 if (r.name == realmName && r.address == realmAddress) {
                     realmId = r.id;
+                    realmBuild = r.build;
                     break;
                 }
             }
-            LOG_INFO("Selected realmId=", realmId);
+            LOG_INFO("Selected realmId=", realmId, " realmBuild=", realmBuild);
         }
 
         uint32_t clientBuild = 12340; // default WotLK
@@ -1366,6 +1368,12 @@ void Application::setupUICallbacks() {
             auto* profile = expansionRegistry_->getActive();
             if (profile) clientBuild = profile->worldBuild;
         }
+        // Prefer realm-reported build when available (e.g. vanilla servers
+        // that report build 5875 in the realm list)
+        if (realmBuild != 0) {
+            clientBuild = realmBuild;
+            LOG_INFO("Using realm-reported build: ", clientBuild);
+        }
         if (gameHandler->connect(host, port, sessionKey, accountName, clientBuild, realmId)) {
             LOG_INFO("Connected to world server, transitioning to character selection");
             setState(AppState::CHARACTER_SELECTION);

src/ui/realm_screen.cpp

@@ -179,10 +179,10 @@ void RealmScreen::render(auth::AuthHandler& authHandler) {
                 ImGui::TextColored(ImVec4(0.4f, 0.9f, 1.0f, 1.0f),
                     " - %d character%s", realm.characters, realm.characters > 1 ? "s" : "");
             }
-            if (realm.hasVersionInfo()) {
+            if (realm.hasVersionInfo() && (realm.majorVersion || realm.build)) {
                 ImGui::SameLine();
-                ImGui::TextDisabled(" v%d.%d.%d",
-                    realm.majorVersion, realm.minorVersion, realm.patchVersion);
+                ImGui::TextDisabled(" v%d.%d.%d (build %d)",
+                    realm.majorVersion, realm.minorVersion, realm.patchVersion, realm.build);
             }
 
             ImGui::Spacing();