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.

Scripts/verify.sh

@@ -87,6 +87,7 @@ required=(
   Tests/SCRAMSHA512Tests.swift
   Tests/AppLockPolicyTests.swift
   Tests/CallHistorySyncTests.swift
+  UITests/TimelineUITests.swift
   Sources/Shared/XMPP/LumaScramSha512Mechanism.swift
   Sources/Shared/XMPP/CallHistorySync.swift
   Sources/Shared/Security/AppLockVault.swift
@@ -389,6 +390,10 @@ grep -q 'let items = pickedMediaItems' Sources/Shared/UI/ChatView.swift || {
   echo "Gallery staging must run on picker dismissal only"
   exit 1
 }
+grep -q 'connectionStatus == .connected' Sources/Shared/Models/AppModel.swift || {
+  echo "Older-history loads must skip silently while disconnected"
+  exit 1
+}
 grep -q 'onDismissRequest' Sources/Shared/UI/SystemPhotoCameraView.swift || {
   echo "The camera picker must request dismissal before background preparation"
   exit 1