fix: use v-show for frequently toggled canvas overlay components

Amp-Thread-ID: https://ampcode.com/threads/T-019cbb69-3404-726a-8888-182193115b88

src/components/graph/NodeTooltip.vue

@@ -1,6 +1,6 @@
 <template>
   <div
-    v-if="tooltipText"
+    v-show="tooltipText"
     ref="tooltipRef"
     class="node-tooltip"
     :style="{ left, top }"
@@ -34,7 +34,8 @@ const left = ref<string>()
 const top = ref<string>()
 
 function hideTooltip() {
-  return (tooltipText.value = '')
+  if (!tooltipText.value) return
+  tooltipText.value = ''
 }
 
 async function showTooltip(tooltip: string | null | undefined) {

src/components/graph/SelectionRectangle.vue

@@ -1,6 +1,6 @@
 <template>
   <div
-    v-if="isVisible"
+    v-show="isVisible"
     class="pointer-events-none absolute z-9999 border border-blue-400 bg-blue-500/20"
     :style="rectangleStyle"
   />