Feed resilience, clearer empty states, and read/unread

- Don't blank the feed on refresh: keep current stories until new data
  arrives, and ignore benign URLError.cancelled (-999) so a network blip
  no longer wipes the list. Coalesce WebSocket story.created bursts into a
  single debounced refresh.
- Empty state now distinguishes polling, couldn't-reach-server (with the
  error + host + Retry), offline, and genuinely-empty.
- Track read stories in SwiftData (ReadStory); mark a story read when opened
  and drop/dim its signal stripe across the feed and Latest/Saved/Search.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Jarvis/Views/Home/StoryRowView.swift

@@ -7,12 +7,14 @@ struct StoryRowView: View {
     let story: StorySummary
     /// True when the story's articles are cached in SwiftData (offline-ready).
     var isCached: Bool = false
+    /// True once the story has been opened — drops the orange stripe and dims it.
+    var isRead: Bool = false
 
     private var sourceNames: [String] { story.sources.map(\.name) }
 
     var body: some View {
         HStack(alignment: .top, spacing: 0) {
-            SignalStripe(score: story.signalScore)
+            SignalStripe(score: story.signalScore, muted: isRead)
 
             VStack(alignment: .leading, spacing: 9) {
                 // Title (+ cached dot)
@@ -51,6 +53,7 @@ struct StoryRowView: View {
                 .padding(.trailing, 16)
                 .padding(.top, 16)
         }
+        .opacity(isRead ? 0.55 : 1)
         .frame(maxWidth: .infinity, alignment: .leading)
         .background(Color.black)
         .overlay(alignment: .bottom) {