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/modal/SuggestionsPanel.vue

@@ -38,6 +38,7 @@
 </template>
 
 <script setup>
+import { toast } from '../../utils/toast.js'
 import { computed, ref, watch } from 'vue'
 import { useSuggestionsStore, CATEGORY_LABELS } from '../../stores/suggestions.js'
 import SuggestionsCategoryGroup from './SuggestionsCategoryGroup.vue'
@@ -57,7 +58,7 @@ watch(() => props.imageId, (id) => { if (id != null) store.load(id) }, { immedia
 
 async function onAccept(s) {
   try { await store.accept(s) }
-  catch (e) { window.__fcToast?.({ text: `Accept failed: ${e.message}`, type: 'error' }) }
+  catch (e) { toast({ text: `Accept failed: ${e.message}`, type: 'error' }) }
 }
 
 const aliasDialog = ref(false)
@@ -68,7 +69,7 @@ async function onAliasConfirm(canonicalTagId) {
     await store.aliasAccept(aliasTarget.value, canonicalTagId)
     aliasDialog.value = false
   } catch (e) {
-    window.__fcToast?.({ text: `Alias failed: ${e.message}`, type: 'error' })
+    toast({ text: `Alias failed: ${e.message}`, type: 'error' })
   }
 }
 </script>