add app open/close animations using RCSS

- app-opening: 0.2s quadratic-out scale from 0.9 to 1.0
- app-closing: 0.15s quadratic-in scale from 1.0 to 0.9
- Avoided back-out easing to prevent flickering

src/main/assets/apps/shell/shell.lua

@@ -60,9 +60,6 @@ function loadAppContent_internal(app_id, app_path, skip_animation)
 
     -- Load app content using C++ function
     if loadAppContent then
-        -- Hide container before loading to prevent flash
-        app_container:SetClass("app-hidden", true)
-
         local success = loadAppContent(app_container, app_path)
         showLoading(false)
 
@@ -71,8 +68,17 @@ function loadAppContent_internal(app_id, app_path, skip_animation)
             current_app_path = app_path
             print("[Shell] App loaded: " .. app_id)
 
-            -- Show container after content is loaded
-            app_container:SetClass("app-hidden", false)
+            -- Play opening animation (unless skipped for initial load)
+            if not skip_animation then
+                app_container:SetClass("app-closing", false)
+                app_container:SetClass("app-opening", true)
+                -- Remove animation class after it completes
+                if setTimeout then
+                    setTimeout(function()
+                        app_container:SetClass("app-opening", false)
+                    end, 200)
+                end
+            end
 
             -- If home was loaded, populate apps dynamically
             if app_id == "home" then
@@ -132,10 +138,19 @@ end
 
 -- ===== NAVIGATION =====
 
--- Execute callback for navigation (animations removed to fix flash)
+-- Play closing animation then execute callback
 local function playCloseAnimation(callback)
-    -- Just execute callback immediately - loadAppContent handles hiding
-    if callback then callback() end
+    if app_container and setTimeout then
+        app_container:SetClass("app-opening", false)
+        app_container:SetClass("app-closing", true)
+        -- Wait for animation to complete before loading new content
+        setTimeout(function()
+            if callback then callback() end
+        end, 150)
+    else
+        -- No animation support, execute immediately
+        if callback then callback() end
+    end
 end
 
 -- Go back to previous app

src/main/assets/apps/shell/shell.rml

@@ -51,9 +51,37 @@
             background-color: #121212;
         }
 
-        /* App visibility - simple hide/show without complex animations */
-        .app-hidden {
+        /* App open/close animations */
+        .app-opening {
+            animation: 0.2s quadratic-out app-open;
+        }
+
+        .app-closing {
+            animation: 0.15s quadratic-in app-close;
             opacity: 0;
+            transform: scale(0.9);
+        }
+
+        @keyframes app-open {
+            from {
+                opacity: 0;
+                transform: scale(0.9);
+            }
+            to {
+                opacity: 1;
+                transform: scale(1.0);
+            }
+        }
+
+        @keyframes app-close {
+            from {
+                opacity: 1;
+                transform: scale(1.0);
+            }
+            to {
+                opacity: 0;
+                transform: scale(0.9);
+            }
         }
 
         /* System navigation bar at bottom - always visible */