stop the disconnected-history alert from blocking scrolling

- Skip older-history loads silently while the connection is down:
  the trigger previously failed with "not connected", popped the
  global alert over the timeline and froze scrolling until dismissed.
- Accept fast reply-swipe flicks whose end state is clearly leftward
  even without an intermediate horizontal lock, while scroll-owned
  touches still never activate the swipe.
- Add a seeded-chat UI test mode (launch argument), accessibility
  identifiers and a LumaUITests target with timeline scroll and reply
  swipe tests; guard the fix in verify.sh.

Sources/Shared/UI/ChatView.swift

@@ -628,6 +628,7 @@ struct ChatView: View {
                     .onChange(of: messages) { _, newMessages in
                         rebuildTimelineEntries(from: newMessages)
                     }
+                    .accessibilityIdentifier("chat-timeline")
                     #if os(macOS)
                         .onPreferenceChange(TimelineBottomYPreferenceKey.self) {
                             bottomY in
@@ -1851,6 +1852,7 @@ struct ChatView: View {
             .buttonStyle(.plain)
             .accessibilityLabel("Отменить ответ")
         }
+        .accessibilityIdentifier("reply-banner")
         //        .padding(.horizontal, 12)
         //        .padding(.vertical, 8)
         //        .background(