feat: add smooth slide-out animation for mobile panel closing

Added matching slide-out animation when closing the mobile panel to
match the smooth slide-in animation on opening:

CSS changes (style.css):
- Add .rpg-mobile-closing class with rpgSlideOutToRight animation
- Create @keyframes rpgSlideOutToRight (0.3s ease-in-out)
- Panel slides smoothly off-screen to right before hiding

JavaScript changes (index.js):
- Add closeMobilePanelWithAnimation() helper function
- Use animationend event to wait for animation before hiding
- Replace all instant removeClass() calls with helper function
- Maintains smooth 0.3s animation timing matching slide-in

Implementation details:
- Helper function adds .rpg-mobile-closing class
- Waits for CSS animation to complete via animationend event
- Then removes closing class and overlay
- All close operations now use this helper for consistency

Result: Panel now smoothly slides in AND out with matching 0.3s
animations. No more jarring instant disappearance on close.

style.css

@@ -3057,6 +3057,13 @@ body:has(.rpg-panel.rpg-position-left) #sheld {
         animation: rpgSlideInFromRight 0.3s ease-in-out;
     }
 
+    /* Closing animation - slide out to right */
+    .rpg-panel.rpg-mobile-closing {
+        display: block !important;
+        z-index: 50;
+        animation: rpgSlideOutToRight 0.3s ease-in-out;
+    }
+
     /* Slide-in animation from right */
     @keyframes rpgSlideInFromRight {
         from {
@@ -3067,6 +3074,16 @@ body:has(.rpg-panel.rpg-position-left) #sheld {
         }
     }
 
+    /* Slide-out animation to right */
+    @keyframes rpgSlideOutToRight {
+        from {
+            transform: translateX(0);
+        }
+        to {
+            transform: translateX(100%);
+        }
+    }
+
     /* Disable collapsed state on mobile */
     .rpg-panel.rpg-collapsed {
         max-width: 100dvw !important;