Fix CustomSelect panel to left-align by default, right-align only when it would overflow the viewport

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

assets/css/ui.css

@@ -475,8 +475,8 @@
 .cs-panel {
   position: absolute;
   top: calc(100% + 4px);
-  right: 0;           /* right edge flushes with button's right edge */
-  left: auto;
+  left: 0;            /* left edge flushes with button's left edge by default */
+  right: auto;
   z-index: 1000;
   background: #fffcf2;
   border: 1.5px solid #c9b08a;
@@ -487,6 +487,12 @@
   overflow: hidden;
 }
 
+/* Flip panel to right-align when left-align would overflow the viewport */
+.cs-panel.cs-panel--right {
+  left: auto;
+  right: 0;
+}
+
 /* Each option row */
 .cs-option {
   display: block;