fix: re-mount DOM widget elements after leaving Linear mode (#8753)

## Summary

LinearView renders its own WidgetDOM instances which steal the
widget.element via replaceChildren. When LinearView unmounts
(v-if="linearMode") the element is removed from the DOM entirely.
The canvas-side WidgetDOM stays mounted but its container is now empty,
so DOM widgets (e.g. Three.js scenes) disappear.

Watch canvasStore.linearMode and reclaim the element when switching back
from Linear to Canvas mode.

## Screenshots (if applicable)
before


https://github.com/user-attachments/assets/78cea2bc-c4b3-4b21-bdb3-a521bb0d3062


after


https://github.com/user-attachments/assets/8f92c44d-9514-4001-bbdb-bc4c80468ed7

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-8753-fix-re-mount-DOM-widget-elements-after-leaving-Linear-mode-3026d73d3650810b8968eff13dc84e9a)
by [Unito](https://www.unito.io)

src/components/graph/widgets/DomWidget.vue

@@ -18,7 +18,7 @@
 </template>
 
 <script setup lang="ts">
-import { useElementBounding, useEventListener } from '@vueuse/core'
+import { useElementBounding, useEventListener, whenever } from '@vueuse/core'
 import type { CSSProperties } from 'vue'
 import { computed, nextTick, onMounted, ref, watch } from 'vue'
 
@@ -180,6 +180,8 @@ watch(
     mountElementIfVisible()
   }
 )
+
+whenever(() => !canvasStore.linearMode, mountElementIfVisible)
 </script>
 
 <style scoped>

src/renderer/extensions/vueNodes/widgets/components/WidgetDOM.vue

@@ -1,4 +1,5 @@
 <script setup lang="ts">
+import { whenever } from '@vueuse/core'
 import { onMounted, ref } from 'vue'
 
 import { useCanvasStore } from '@/renderer/core/canvas/canvasStore'
@@ -13,15 +14,24 @@ const props = defineProps<{
 
 const domEl = ref<HTMLElement>()
 
-const { canvas } = useCanvasStore()
-onMounted(() => {
+const canvasStore = useCanvasStore()
+const { canvas } = canvasStore
+
+function mountWidgetElement() {
   if (!domEl.value) return
   const node = canvas?.graph?.getNodeById(props.nodeId) ?? undefined
   if (!node) return
   const widget = node.widgets?.find((w) => w.name === props.widget.name)
   if (!widget || !isDOMWidget(widget)) return
+  if (domEl.value.contains(widget.element)) return
   domEl.value.replaceChildren(widget.element)
+}
+
+onMounted(() => {
+  mountWidgetElement()
 })
+
+whenever(() => !canvasStore.linearMode, mountWidgetElement)
 </script>
 <template>
   <div ref="domEl" @pointerdown.stop @pointermove.stop @pointerup.stop />