fix: hide empty actionbar container and relocate error border to floating actionbar (#9657)

## Summary
When the actionbar is floating and has no docked buttons, the container
is now hidden (zero-width, transparent border) to avoid showing an empty
rounded box. Additionally, the error/destructive border is now applied
to the floating actionbar panel itself (via `ComfyActionbar`) instead of
the container, so it appears in the correct location when floating.

## Changes
- **TopMenuSection**: Added `hasDockedButtons` and
`isActionbarContainerEmpty` computed properties to detect when the
docked container has no visible buttons; `actionbarContainerClass`
computed hides the container by collapsing it when empty and floating,
while preserving the legacy drop zone via `:has(.border-dashed)` CSS
selector
- **TopMenuSection**: Error border
(`border-destructive-background-hover`) is now only applied to the
docked container when the actionbar is **not** floating
- **ComfyActionbar**: Accepts new `hasAnyError` prop and applies the
error border to the floating panel's `panelClass` when floating

## Review Focus
- The `has-[.border-dashed]` CSS selector restores the container visuals
when a legacy drag-target element is present inside it — verify this
works as expected
- Error border placement: docked mode shows border on container,
floating mode shows border on the fixed panel

## Screenshots


https://github.com/user-attachments/assets/75caabac-e391-4bfd-b4dc-62d564e55d37

src/components/actionbar/ComfyActionbar.vue

@@ -119,9 +119,14 @@ import { cn } from '@/utils/tailwindUtil'
 
 import ComfyRunButton from './ComfyRunButton'
 
-const { topMenuContainer, queueOverlayExpanded = false } = defineProps<{
+const {
+  topMenuContainer,
+  queueOverlayExpanded = false,
+  hasAnyError = false
+} = defineProps<{
   topMenuContainer?: HTMLElement | null
   queueOverlayExpanded?: boolean
+  hasAnyError?: boolean
 }>()
 
 const emit = defineEmits<{
@@ -435,7 +440,12 @@ const panelClass = computed(() =>
     isDragging.value && 'pointer-events-none select-none',
     isDocked.value
       ? 'static border-none bg-transparent p-0'
-      : 'fixed shadow-interface'
+      : [
+          'fixed shadow-interface',
+          hasAnyError
+            ? 'border-destructive-background-hover'
+            : 'border-interface-stroke'
+        ]
   )
 )
 </script>