Use a real tab strip for servers instead of a button bar

ServerTabPane replaces ServerTabBar: the views live in a JTabbedPane
whose strip sits under the toolbar, with the native tab shapes and the
same look as the chat tabs. Each tab carries its server name, the
microphone marker and a close glyph. With a single connection the
server view is mounted directly, so the strip appears only once a
second server is open.

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

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

@@ -0,0 +1,140 @@
+package com.ts3client.ui;
+
+import javax.swing.BorderFactory;
+import javax.swing.JButton;
+import javax.swing.JComponent;
+import javax.swing.JLabel;
+import javax.swing.JPanel;
+import javax.swing.JTabbedPane;
+import java.awt.BorderLayout;
+import java.awt.Dimension;
+import java.awt.FlowLayout;
+import java.awt.Insets;
+import java.awt.event.MouseAdapter;
+import java.awt.event.MouseEvent;
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Container for the open server connections. With a single connection the
+ * server view fills the window as it always did; from the second connection on
+ * the views move into a {@link JTabbedPane} whose tab strip sits directly under
+ * the toolbar.
+ */
+final class ServerTabPane extends JPanel {
+
+    interface Listener {
+        void selectTab(ServerTab tab);
+
+        void closeTab(ServerTab tab);
+    }
+
+    private final Listener listener;
+    private final JTabbedPane tabbed = new JTabbedPane();
+    private final List<ServerTab> tabs = new ArrayList<>();
+
+    /** True while the tab strip is in use, i.e. more than one connection is open. */
+    private boolean tabbedMode;
+    /** Suppresses selection callbacks while we rearrange the pane ourselves. */
+    private boolean updating;
+
+    ServerTabPane(Listener listener) {
+        super(new BorderLayout());
+        this.listener = listener;
+        tabbed.setTabLayoutPolicy(JTabbedPane.SCROLL_TAB_LAYOUT);
+        tabbed.setFocusable(false);
+        tabbed.addChangeListener(e -> {
+            if (updating) return;
+            int i = tabbed.getSelectedIndex();
+            if (i >= 0 && i < tabs.size()) listener.selectTab(tabs.get(i));
+        });
+    }
+
+    void addTab(ServerTab tab) {
+        tabs.add(tab);
+        relayout();
+    }
+
+    void removeTab(ServerTab tab) {
+        tabs.remove(tab);
+        relayout();
+    }
+
+    void setSelected(ServerTab tab) {
+        int i = tabs.indexOf(tab);
+        if (!tabbedMode || i < 0 || tabbed.getSelectedIndex() == i) return;
+        updating = true;
+        try {
+            tabbed.setSelectedIndex(i);
+        } finally {
+            updating = false;
+        }
+    }
+
+    /** Refreshes the tab labels; {@code micTab} is marked as owning the microphone. */
+    void refresh(ServerTab micTab) {
+        if (!tabbedMode) return;
+        for (int i = 0; i < tabs.size(); i++) {
+            ServerTab tab = tabs.get(i);
+            tabbed.setTitleAt(i, tab.title());
+            tabbed.setToolTipTextAt(i, tab.status());
+            tabbed.setTabComponentAt(i, buildTabComponent(tab, tab == micTab));
+        }
+    }
+
+    /**
+     * Moves the views between the plain single-server layout and the tabbed one,
+     * keeping whatever is currently selected on screen.
+     */
+    private void relayout() {
+        boolean wantTabs = tabs.size() > 1;
+        updating = true;
+        try {
+            removeAll();
+            tabbed.removeAll();
+            if (wantTabs) {
+                for (ServerTab tab : tabs) tabbed.addTab(tab.title(), tab.component());
+                add(tabbed, BorderLayout.CENTER);
+            } else if (!tabs.isEmpty()) {
+                add(tabs.get(0).component(), BorderLayout.CENTER);
+            }
+            tabbedMode = wantTabs;
+        } finally {
+            updating = false;
+        }
+        revalidate();
+        repaint();
+    }
+
+    /** A tab's label: title, microphone marker and a close button. */
+    private JComponent buildTabComponent(ServerTab tab, boolean hasMic) {
+        JPanel cell = new JPanel(new FlowLayout(FlowLayout.LEFT, 4, 0));
+        cell.setOpaque(false);
+        cell.setBorder(BorderFactory.createEmptyBorder(1, 0, 1, 0));
+
+        JLabel label = new JLabel(tab.title(), hasMic ? Icons.micActive() : null, JLabel.LEADING);
+        label.setFont(Theme.UI_FONT);
+        label.setToolTipText(hasMic ? "Speaking on this server" : tab.status());
+        // A label with a tooltip swallows mouse events, so select the tab explicitly.
+        label.addMouseListener(new MouseAdapter() {
+            @Override
+            public void mousePressed(MouseEvent e) {
+                listener.selectTab(tab);
+            }
+        });
+        cell.add(label);
+
+        JButton close = new JButton("✕");
+        close.setFont(Theme.UI_FONT);
+        close.setFocusable(false);
+        close.setBorder(BorderFactory.createEmptyBorder());
+        close.setContentAreaFilled(false);
+        close.setMargin(new Insets(0, 0, 0, 0));
+        close.setForeground(Theme.CHAT_SYSTEM);
+        close.setPreferredSize(new Dimension(14, 14));
+        close.setToolTipText("Close this connection");
+        close.addActionListener(e -> listener.closeTab(tab));
+        cell.add(close);
+        return cell;
+    }
+}