fix: only show mobile refresh FAB when panel open AND in Separate mode

The mobile refresh button was always visible on mobile. It should only
appear when BOTH conditions are met:
- RPG panel is open
- Generation mode is Separate (not Together)

Changes:
- Added opacity: 0 and pointer-events: none to base .rpg-mobile-refresh
- CSS shows button when panel open AND not .rpg-hidden-mode class
- Updated updateGenerationModeUI() to toggle .rpg-hidden-mode on mobile button
- Together mode: adds .rpg-hidden-mode class (keeps button hidden)
- Separate mode: removes .rpg-hidden-mode class (allows CSS to show it)

Result: Mobile refresh FAB only appears when panel is open AND in
Separate mode. Stays hidden when panel closed OR in Together mode.

style.css

@@ -3328,6 +3328,9 @@ body:has(.rpg-panel.rpg-position-left) #sheld {
     user-select: none;
     -webkit-user-select: none;
     will-change: top, left;
+    /* Hidden by default - shown when panel open AND separate mode */
+    opacity: 0;
+    pointer-events: none;
 }
 
 .rpg-mobile-refresh.dragging {
@@ -3387,17 +3390,23 @@ body:has(.rpg-panel.rpg-position-left) #sheld {
         display: flex;
     }
 
-    /* Show the mobile FAB refresh button */
+    /* Show the mobile FAB refresh button (but hidden by opacity) */
     .rpg-mobile-refresh {
         display: flex;
     }
 
+    /* Show refresh button when panel is open AND not hidden by generation mode */
+    body:has(.rpg-panel.rpg-mobile-open) .rpg-mobile-refresh:not(.rpg-hidden-mode) {
+        opacity: 1;
+        pointer-events: auto;
+    }
+
     /* Hide desktop refresh button on mobile */
     #rpg-manual-update {
         display: none !important;
     }
 
-    /* Hide FAB when panel is open */
+    /* Hide toggle FAB when panel is open */
     body:has(.rpg-panel.rpg-mobile-open) .rpg-mobile-toggle {
         opacity: 0;
         pointer-events: none;