Scale the interface fractionally on Linux

Java2D on X11 (and so under XWayland) truncates its scale to a whole
number, drawing 150 % at 100 %. On Linux, pin Java2D to 1 and hand the
full factor to FlatLaf, taken from XSETTINGS Xft/DPI, KWin's Xwayland
scale or GDK_SCALE, or chosen in Options → Design.

The client's own sizes now go through UIScale: borders, gaps, dialog and
row sizes, icons (rendered at the scaled size, so they stay crisp),
custom-painted components and font sizes in the HTML views.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

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

@@ -1,5 +1,6 @@
 package com.ts3client.ui;
 
+import com.formdev.flatlaf.util.UIScale;
 import com.ts3client.config.Settings;
 import com.ts3client.contacts.ContactStore;
 import com.ts3client.contacts.ContactType;
@@ -168,7 +169,7 @@ public final class ServerTreePanel extends JScrollPane {
             ui.setLeftChildIndent(4);
             ui.setRightChildIndent(10);
         }
-        tree.setRowHeight(20);
+        tree.setRowHeight(UIScale.scale(20));
         tree.setBackground(Theme.treeBg());
         tree.setFont(Theme.uiFont());
         ServerTreeCellRenderer renderer = new ServerTreeCellRenderer(id -> id == selfClientId, contacts, settings);