Tabbed servers: multiple simultaneous connections

Each connection now lives in its own ServerTab with its own tree, info
and chat views plus its own mic-mute, deafen, away and commander state.
MainFrame keeps only the shell (menus, toolbar, status bar) and shows
one tab at a time; the tab bar below the toolbar appears once a second
server is open.

Incoming voice from every connection mixes into the same output — each
connection already renders one line per speaker. Capture is exclusive:
a connection only opens the microphone while it holds it, and a toolbar
button moves it to the visible tab. The mic follows a disconnect to
another connected tab, and push-to-talk drives whoever holds it.

Startup bookmarks are no longer mutually exclusive: every flagged
bookmark opens its own tab.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

ts3-client/swing/src/main/java/com/ts3client/ui/BookmarksDialog.java

@@ -108,7 +108,8 @@ public final class BookmarksDialog extends JDialog {
 
         channel.setToolTipText("Channel path, e.g. \"Lobby/Games\", or a channel id. "
                 + "Leave empty for the server's default channel.");
-        connectOnStartup.setToolTipText("Connect to this server automatically when the client starts.");
+        connectOnStartup.setToolTipText("Connect to this server automatically when the client starts. "
+                + "Several bookmarks may be flagged; each opens its own tab.");
 
         int row = 0;
         addRow(panel, row++, "Label:", label);
@@ -199,12 +200,6 @@ public final class BookmarksDialog extends JDialog {
         editing.channelPassword = new String(channelPassword.getPassword());
         editing.identityId = identity.getSelectedIdentityId();
         editing.connectOnStartup = connectOnStartup.isSelected();
-        // Only one bookmark can be connected to at startup.
-        if (editing.connectOnStartup) {
-            for (Bookmark other : bookmarks.all()) {
-                if (other != editing) other.connectOnStartup = false;
-            }
-        }
         list.repaint();
     }