fix: use grid instead of flex m-auto for BaseViewTemplate centering

Flexbox has a known gotcha where auto margins go negative when content
exceeds the container, pushing content off the top. CSS grid's
place-items-center handles overflow correctly — content centers when it
fits, aligns to top when it doesn't, and scrolls properly. Fixes /connect
still being unscrollable from the previous m-auto attempt.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/views/templates/BaseViewTemplate.vue

@@ -13,8 +13,8 @@
       ref="topMenuRef"
       class="app-drag h-(--comfy-topbar-height) w-full"
     />
-    <div class="flex w-full grow justify-center overflow-auto">
-      <div class="m-auto py-8">
+    <div class="grid w-full grow place-items-center overflow-auto">
+      <div class="py-8">
         <slot />
       </div>
     </div>