fix(clients/android): 3-finger stats tap — re-anchor the scroll centroid on pointer-count changes

The two-or-more-finger scroll path measured its centroid across a VARYING
pointer count: real fingers never land (or lift) in the same input frame, so
the 2→3 transition moved the centroid far past SCROLL_DIV, emitted a phantom
wheel tick to the host, and set `moved` — which disqualified the not-moved tap
classification and made the advertised 3-finger stats-cycle tap unreachable on
real hardware (two-finger right-click survived only because its anchor never
crossed a count change). Re-anchor whenever the finger count changes; genuine
two-finger scrolling is measured between same-count frames exactly as before.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

clients/android/app/src/main/kotlin/io/unom/punktfunk/TouchInput.kt

@@ -127,6 +127,7 @@ internal suspend fun PointerInputScope.streamTouchInput(
         var moved = false
         var maxFingers = 1
         var scrolling = false
+        var scrollCount = 0 // pointer count the scroll centroid is anchored at
         var prevCx = startX
         var prevCy = startY
         var upTime = down.uptimeMillis
@@ -149,11 +150,18 @@ internal suspend fun PointerInputScope.streamTouchInput(
             if (pressed.size > maxFingers) maxFingers = pressed.size
 
             if (pressed.size >= 2) {
-                // Two fingers → scroll by the centroid delta; never move the cursor.
+                // Two+ fingers → scroll by the centroid delta; never move the cursor.
                 val cx = (pressed.sumOf { it.position.x.toDouble() } / pressed.size).toFloat()
                 val cy = (pressed.sumOf { it.position.y.toDouble() } / pressed.size).toFloat()
-                if (!scrolling) {
+                // (Re-)anchor whenever the finger COUNT changes, not just on scroll start: the
+                // centroid of three fingers sits far from the centroid of two, and real fingers
+                // never land (or lift) in the same input frame — so the 2→3 transition would
+                // otherwise read as a scroll notch, sending a phantom wheel tick to the host AND
+                // setting `moved`, which disqualified the tap classification below and made the
+                // 3-finger stats tap unreachable on real hardware.
+                if (!scrolling || pressed.size != scrollCount) {
                     scrolling = true
+                    scrollCount = pressed.size
                     prevCx = cx
                     prevCy = cy
                 }