fix: refine iframe transition timing and default values

- Adjust transition duration to 200ms for smoother crossfade
- Add explicit default values for iframe transform properties
- Simplify transition with 'all' shorthand
- Set explicit transition duration for editor panel

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

src/App.vue

@@ -113,7 +113,7 @@ const renderPreview = async (shouldReloadFromFile = false) => {
           // Swap current frame
           currentFrameIndex.value = currentFrameIndex.value === 1 ? 2 : 1;
           isTransitioning = false;
-        }, 100); // Match CSS transition duration
+        }, 200); // Match CSS transition duration
       }, 50); // Small delay to ensure scroll is set
     }, 200); // Wait for PagedJS
   };
@@ -158,8 +158,10 @@ onMounted(() => renderPreview(true));
   width: 100vw;
   height: 100vh;
   border: none;
-  transition: opacity 0.1s ease-in-out, margin-left ease-in-out var(--curve),
-    transform ease-in-out var(--curve), height ease-in-out var(--curve);
+  margin-left: 0;
+  transform: scale(1) translateY(0);
+  height: 100vh;
+  transition: all 0.2s ease-in-out var(--curve);
 }
 
 .preview-frame.shifted {

src/components/editor/EditorPanel.vue

@@ -85,7 +85,7 @@ nav {
   background-color: var(--color-panel-bg);
   box-shadow: -5px 0px 12px;
 
-  transition: left ease-in-out var(--curve);
+  transition: left 0.3s var(--curve);
 }
 
 .tab-content.open {