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/DownloadsTab.vue

@@ -113,6 +113,7 @@
 </template>
 
 <script setup>
+import { toast } from '../../utils/toast.js'
 import { computed, onMounted, onUnmounted, reactive, ref, watch } from 'vue'
 import { useRoute } from 'vue-router'
 
@@ -167,12 +168,12 @@ async function refresh() {
 async function onRetrySource(source) {
   try {
     await sourcesStore.checkNow(source.id)
-    globalThis.window?.__fcToast?.({ text: `Retry queued for ${source.artist_name || source.platform}`, type: 'success' })
+    toast({ text: `Retry queued for ${source.artist_name || source.platform}`, type: 'success' })
   } catch (e) {
     if (e?.body?.download_event_id) {
-      globalThis.window?.__fcToast?.({ text: 'Already running — see below', type: 'info' })
+      toast({ text: 'Already running — see below', type: 'info' })
     } else {
-      globalThis.window?.__fcToast?.({ text: `Retry failed: ${e?.detail || e?.message || e}`, type: 'error' })
+      toast({ text: `Retry failed: ${e?.detail || e?.message || e}`, type: 'error' })
     }
   } finally {
     await Promise.all([store.loadFailing(), store.loadStats(24), store.loadFirst()])
@@ -199,7 +200,7 @@ async function onRetryAll(sources) {
   const parts = []
   if (ok) parts.push(`${ok} queued`)
   if (conflict) parts.push(`${conflict} already running`)
-  globalThis.window?.__fcToast?.({ text: parts.join(', ') || 'Nothing to retry', type: 'info' })
+  toast({ text: parts.join(', ') || 'Nothing to retry', type: 'info' })
 }
 
 // Live auto-refresh: while any download is queued or running, poll the