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.

Tests/MessageReplySwipeTests.swift

@@ -107,6 +107,13 @@ final class MessageReplySwipeTests: XCTestCase {
         XCTAssertFalse(MessageReplySwipePolicy.canLock(CGSize(width: 40, height: 4)))
     }
 
+    func testCanLockIsUnavailableOnceTheGestureTurnsVertical() {
+        // A scroll that arcs left after travelling down must never lock the
+        // swipe: the vertical travel already exceeds the lock budget.
+        XCTAssertFalse(MessageReplySwipePolicy.canLock(CGSize(width: -30, height: 40)))
+        XCTAssertFalse(MessageReplySwipePolicy.canLock(CGSize(width: -80, height: 60)))
+    }
+
     func testLockedSwipeToleratesVerticalDrift() {
         // Once locked the finger may drift: a 1.17 ratio would be rejected
         // by the 1.6 lock dominance but must still count as a reply swipe.