fix(app): clean up online/offline listeners on Browse unmount (#7213)

fix(app): clean up online/offline listeners on Browse.vue unmount

Browse.vue registers window 'online'/'offline' listeners but never
removes them. Since only LibraryPage is kept alive by the router,
Browse unmounts every time the user navigates away (e.g. into a
project) and remounts on return, leaking a new pair of closures (and
pinning the whole component scope) on window each time. Over a
browsing session this accumulates continuously.

apps/app-frontend/src/pages/Browse.vue

@@ -34,7 +34,7 @@ import {
 } from '@modrinth/ui'
 import { useQuery, useQueryClient } from '@tanstack/vue-query'
 import type { Ref } from 'vue'
-import { computed, ref, shallowRef, watch } from 'vue'
+import { computed, onBeforeUnmount, ref, shallowRef, watch } from 'vue'
 import type { LocationQuery } from 'vue-router'
 import { useRoute, useRouter } from 'vue-router'
 
@@ -530,13 +530,20 @@ const {
 })
 
 const offline = ref(!navigator.onLine)
-window.addEventListener('offline', () => {
+const handleOffline = () => {
 	debugLog('went offline')
 	offline.value = true
-})
+}
-window.addEventListener('online', () => {
+const handleOnline = () => {
 	debugLog('went online')
 	offline.value = false
+}
+window.addEventListener('offline', handleOffline)
+window.addEventListener('online', handleOnline)
+
+onBeforeUnmount(() => {
+	window.removeEventListener('offline', handleOffline)
+	window.removeEventListener('online', handleOnline)
 })
 
 const messages = defineMessages({