Use one base font size and a per-profile startup design

JavaFX picks a 13px default font on macOS and Linux but 12px on
Windows, so labels in fixed-size controls were cut off outside
Windows. Both stylesheets now set 12px on the root.

Each operator profile now chooses light or dark mode for startup on
the GUI settings tab. The Windows menu entries remain a quick switch
for the running session. All windows, including the update window
and the top candidates list, follow the design, and the main window
no longer starts light while the station map starts dark.

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

src/main/resources/KST4ContestDefaultDay.css

@@ -1,3 +1,8 @@
+.root {
+    /* Same base font size on all platforms: macOS/Linux default to 13px, Windows to 12px. */
+    -fx-font-size: 12px;
+}
+
 .button:pressed {
     -fx-border-color: #ff0000;
 }