Integrated tab bar UI elements (#7853)

## Summary

The current help / feedback is often overlooked by users, this adds a
setting that makes it more visible moving it up into the tab bar and
moves the user login/profile button out of the "action bar" into the tab
bar.

## Changes
- Add 'Comfy.UI.TabBarLayout' setting with Default/Integrated options
- Move Help & User controls to tab bar when Integrated mode is enabled
- Extract help center logic into shared useHelpCenter composable

## Screenshots (if applicable)

<img width="515" height="540" alt="image"
src="https://github.com/user-attachments/assets/c9e6057f-4fb1-4da6-b25d-9df4b19be31a"
/>
<img width="835" height="268" alt="image"
src="https://github.com/user-attachments/assets/24afc0e8-97eb-45cf-af86-15a9b464e9a8"
/>

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-7853-Integrated-tab-bar-UI-elements-2df6d73d365081b1beb8f7c641c2fa43)
by [Unito](https://www.unito.io)

---------

Co-authored-by: GitHub Action <action@github.com>
Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

src/components/topbar/TopMenuHelpButton.vue

@@ -0,0 +1,21 @@
+<template>
+  <Button
+    class="comfy-help-center-btn relative text-base-foreground"
+    variant="textonly"
+    @click="toggleHelpCenter"
+  >
+    {{ $t('menu.helpAndFeedback') }}
+    <i class="icon-[lucide--circle-help] ml-0.5" />
+    <span
+      v-if="shouldShowRedDot"
+      class="absolute top-[7px] right-[7px] size-1.5 rounded-full bg-[#ff3b30]"
+    />
+  </Button>
+</template>
+
+<script setup lang="ts">
+import Button from '@/components/ui/button/Button.vue'
+import { useHelpCenter } from '@/composables/useHelpCenter'
+
+const { shouldShowRedDot, toggleHelpCenter } = useHelpCenter('topbar')
+</script>