fix(ios): reduce back-to-latest button sensitivity

ios/Packages/HapiKit/Sources/HapiUI/Chat/TranscriptBottomProximity.swift

@@ -0,0 +1,18 @@
+/// Presentation-only hysteresis. Being close enough to hide the latest
+/// button never opts the reader back into tail following.
+struct TranscriptBottomProximity {
+    private(set) var isAwayFromBottom = false
+
+    mutating func update(bottomDistance: Double, followsTail: Bool) {
+        guard !followsTail else {
+            isAwayFromBottom = false
+            return
+        }
+        let distance = max(0, bottomDistance)
+        if isAwayFromBottom {
+            if distance <= 24 { isAwayFromBottom = false }
+        } else if distance >= 80 {
+            isAwayFromBottom = true
+        }
+    }
+}