fix(fc3b): SourceFormDialog + SubscriptionsView read platforms store; drop sources.loadPlatforms

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/views/SubscriptionsView.vue

@@ -52,12 +52,14 @@
 import { computed, onMounted, ref, watch } from 'vue'
 import { useRoute } from 'vue-router'
 import { useSourcesStore } from '../stores/sources.js'
+import { usePlatformsStore } from '../stores/platforms.js'
 import ArtistSection from '../components/subscriptions/ArtistSection.vue'
 import SourceFormDialog from '../components/subscriptions/SourceFormDialog.vue'
 import ArtistCreateDialog from '../components/subscriptions/ArtistCreateDialog.vue'
 
 const route = useRoute()
 const store = useSourcesStore()
+const platformsStore = usePlatformsStore()
 
 const artistFilter = computed(() => {
   const raw = route.query.artist_id
@@ -73,7 +75,7 @@ const showArtistDialog = ref(false)
 
 async function refresh() {
   await store.loadAll()
-  await store.loadPlatforms()
+  await platformsStore.loadAll()
   if (artistFilter.value != null) {
     openSections.value = new Set([artistFilter.value])
     expandAll.value = false