refactor(dry-F2): centralize shared UI primitives (relative-time, toast, download-status)

- utils/date.js: add formatRelative(iso, {future,nullText}); migrate 6 sites
  (SourceRow, SubscriptionsTab, SourceHealthDot, SchedulerStatusBar +
  thin adapters in BackupRunsTable/SystemActivityTab for their '—' null text).
  PostCard (30d->absolute) and CredentialCard (mo/y buckets) intentionally
  keep bespoke formatters.
- utils/toast.js: toast(opts) wraps the globalThis.window?.__fcToast?.(...)
  incantation; migrate 63 call sites across 24 files.
- utils/downloadStatus.js: single source for the download-event status enum
  -> label/color/icon; collapse the 3 duplicate maps (DownloadStatChips,
  DownloadsFilterPopover, DownloadEventRow).

Net -33 lines. Platform metadata was already centralized in platformColor.js.

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

frontend/src/components/subscriptions/SubscriptionsTab.vue

@@ -199,6 +199,7 @@
 </template>
 
 <script setup>
+import { toast } from '../../utils/toast.js'
 import { computed, onMounted, onUnmounted, ref, watch } from 'vue'
 import { useRoute, useRouter } from 'vue-router'
 import { useSourcesStore } from '../../stores/sources.js'
@@ -210,6 +211,7 @@ import SourceFormDialog from './SourceFormDialog.vue'
 import ArtistCreateDialog from './ArtistCreateDialog.vue'
 import PlatformChip from './PlatformChip.vue'
 import SchedulerStatusBar from './SchedulerStatusBar.vue'
+import { formatRelative } from '../../utils/date.js'
 
 const ITEMS_PER_PAGE_OPTIONS = [
   { value: 25, title: '25' },
@@ -365,16 +367,6 @@ function pickWorstSource(sources, threshold) {
   return sources.reduce((worst, s) => (level(s) > level(worst) ? s : worst), sources[0])
 }
 
-function formatRelative(iso) {
-  if (!iso) return 'Never'
-  const then = new Date(iso).getTime()
-  const diff = (Date.now() - then) / 1000
-  if (diff < 60) return `${Math.floor(diff)}s ago`
-  if (diff < 3600) return `${Math.floor(diff / 60)}m ago`
-  if (diff < 86400) return `${Math.floor(diff / 3600)}h ago`
-  return `${Math.floor(diff / 86400)}d ago`
-}
-
 function onRowClick(_evt, { item }) {
   const key = item.key
   const idx = expanded.value.indexOf(key)
@@ -419,19 +411,19 @@ function onArtistCreated(artist) {
 async function onCheck(source) {
   try {
     const body = await store.checkNow(source.id)
-    globalThis.window?.__fcToast?.({
+    toast({
       text: `Check enqueued (event #${body.download_event_id})`,
       type: 'success',
     })
   } catch (e) {
     if (e?.body?.download_event_id) {
-      globalThis.window?.__fcToast?.({
+      toast({
         text: 'Already running — see Downloads',
         type: 'info',
       })
       router.push({ path: '/subscriptions', query: { tab: 'downloads', source_id: source.id } })
     } else {
-      globalThis.window?.__fcToast?.({
+      toast({
         text: `Check failed: ${e?.detail || e?.message || e}`,
         type: 'error',
       })
@@ -454,7 +446,7 @@ async function checkAll(group) {
   const parts = []
   if (ok) parts.push(`${ok} queued`)
   if (conflict) parts.push(`${conflict} already running`)
-  globalThis.window?.__fcToast?.({
+  toast({
     text: parts.join(', ') || 'Nothing to check (no enabled sources)',
     type: 'info',
   })
@@ -481,7 +473,7 @@ async function bulkSetEnabled(enabled) {
     }
   }
   await refresh()
-  globalThis.window?.__fcToast?.({
+  toast({
     text: `${changed} source${changed === 1 ? '' : 's'} ${enabled ? 'enabled' : 'disabled'}`,
     type: 'success',
   })
@@ -504,7 +496,7 @@ async function bulkDelete() {
     }
   }
   await refresh()
-  globalThis.window?.__fcToast?.({
+  toast({
     text: `${deleted} source${deleted === 1 ? '' : 's'} deleted`,
     type: 'success',
   })