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.

Luma.xcodeproj/xcshareddata/xcschemes/Luma.xcscheme

@@ -64,6 +64,17 @@
                ReferencedContainer = "container:Luma.xcodeproj">
             </BuildableReference>
          </TestableReference>
+         <TestableReference
+            skipped = "NO"
+            parallelizable = "NO">
+            <BuildableReference
+               BuildableIdentifier = "primary"
+               BlueprintIdentifier = "A086B6D25E7969CB643F1C8A"
+               BuildableName = "LumaUITests.xctest"
+               BlueprintName = "LumaUITests"
+               ReferencedContainer = "container:Luma.xcodeproj">
+            </BuildableReference>
+         </TestableReference>
       </Testables>
       <CommandLineArguments>
       </CommandLineArguments>