fix: use staging platform URL for usage history link (#8056)

## Summary

Uses `getComfyPlatformBaseUrl()` for the usage history link so it
correctly points to `stagingplatform.comfy.org` on staging builds
instead of being hardcoded to `platform.comfy.org`.

## Changes

- Added `usageHistoryUrl` computed that uses `getComfyPlatformBaseUrl()`
- Updated template to use dynamic `:href` binding

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-8056-fix-use-staging-platform-URL-for-usage-history-link-2e86d73d36508186a845ffd84e5caaf2)
by [Unito](https://www.unito.io)

---------

Co-authored-by: GitHub Action <action@github.com>

src/platform/cloud/subscription/components/SubscriptionPanel.vue

@@ -156,7 +156,7 @@
 
                   <div class="flex items-center justify-between">
                     <a
-                      href="https://platform.comfy.org/profile/usage"
+                      :href="usageHistoryUrl"
                       target="_blank"
                       rel="noopener noreferrer"
                       class="text-sm underline text-center text-muted"
@@ -274,6 +274,7 @@ import CloudBadge from '@/components/topbar/CloudBadge.vue'
 import Button from '@/components/ui/button/Button.vue'
 import { useFirebaseAuthActions } from '@/composables/auth/useFirebaseAuthActions'
 import { useExternalLink } from '@/composables/useExternalLink'
+import { getComfyPlatformBaseUrl } from '@/config/comfyApi'
 import SubscribeButton from '@/platform/cloud/subscription/components/SubscribeButton.vue'
 import { useSubscription } from '@/platform/cloud/subscription/composables/useSubscription'
 import { useSubscriptionActions } from '@/platform/cloud/subscription/composables/useSubscriptionActions'
@@ -314,6 +315,9 @@ const tierKey = computed(() => {
 const tierPrice = computed(() =>
   getTierPrice(tierKey.value, isYearlySubscription.value)
 )
+const usageHistoryUrl = computed(
+  () => `${getComfyPlatformBaseUrl()}/profile/usage`
+)
 
 const refillsDate = computed(() => {
   if (!subscriptionStatus.value?.renewal_date) return ''