Add Master Volume slider, status bar toggle, and toolbar customization menu

The toolbar now has a right-click menu to hide/show the status bar and
a short Master Volume slider (drag or scroll) that multiplies both
voice and notification volume via new Settings.effectiveOutputVolume()/
effectiveSoundVolume() helpers.

Also splits MainFrame's toolbar, menu bar and status bar construction
into their own MainToolbar/MainMenuBar/StatusBar classes, each talking
back to MainFrame only through a Listener interface.

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

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

@@ -0,0 +1,36 @@
+package com.ts3client.ui;
+
+import javax.swing.BorderFactory;
+import javax.swing.JLabel;
+import javax.swing.JPanel;
+import java.awt.BorderLayout;
+
+/** The strip at the bottom of the window: connection status on the left, codec info on the right. */
+final class StatusBar extends JPanel {
+
+    private final JLabel statusLabel = new JLabel("Not connected");
+    private final JLabel codecLabel = new JLabel();
+
+    StatusBar() {
+        super(new BorderLayout());
+        setBackground(Theme.STATUS_BG);
+        setBorder(BorderFactory.createEmptyBorder(3, 8, 3, 8));
+        statusLabel.setFont(Theme.UI_FONT);
+        codecLabel.setFont(Theme.UI_FONT);
+        codecLabel.setForeground(Theme.CHAT_SYSTEM);
+        add(statusLabel, BorderLayout.WEST);
+        add(codecLabel, BorderLayout.EAST);
+    }
+
+    void setStatus(String text) {
+        statusLabel.setText(text);
+    }
+
+    void setCodec(String text) {
+        codecLabel.setText(text);
+    }
+
+    String codecText() {
+        return codecLabel.getText();
+    }
+}