feat: sync read/unread state to backend with persistent device ID

- APIClient: generate and persist a stable device UUID (jarvis.device.id
  in UserDefaults); attach as X-Jarvis-Device-Id header on every request
- Add markStoryRead / markStoryUnread — POST/DELETE /stories/:id/read with
  device_id, read_at, and source fields
- Wire both calls into all three read-toggle sites: SignalFeedView,
  ArticleReaderView, StoryDetailView
- Add postVoid helper for fire-and-forget POST calls (no response body needed)
- Pass include_read param on stories fetch for future server-side filtering
- CacheMaintenance: recentHours 84→72 (mirrors backend 72h story window);
  markerHours 96→192 so read suppression survives a full weekly news cycle

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Jarvis/Views/Reader/ArticleReaderView.swift

@@ -431,8 +431,10 @@ struct ArticleReaderView: View {
         if let row = (try? modelContext.fetch(
             FetchDescriptor<ReadStory>(predicate: #Predicate { $0.id == id })))?.first {
             modelContext.delete(row)
+            Task { try? await APIClient.shared.markStoryUnread(id: id) }
         } else {
             modelContext.insert(ReadStory(id: id))
+            Task { try? await APIClient.shared.markStoryRead(id: id) }
         }
         try? modelContext.save()
     }