fix(ios): drive gesture pinch via two-finger synthesis instead of single-finger drag (#634)

On iOS the runner lowered `pinch` to performCoordinatePinch — a tap() then a
single-finger press(forDuration:thenDragTo:). React Native reads that as a pan,
so the pinch scale never changes (reported in #629: scale stays 1.00).

Route iOS pinch through the existing two-finger XCTest synthesis path
(transformGesture / RunnerSynthesizedGesture) with zero translation and rotation,
so RN's pinch recognizer fires. macOS keeps the coordinate path.

Validated on iPhone 17 Pro against examples/test-app: the gesture-lab.ad oracle
now passes 1/1 (fling/pan/pinch/rotate); it previously failed at the pinch step.

Refs #629

ios-runner/AgentDeviceRunner/AgentDeviceRunnerUITests/RunnerTests+Interaction.swift

@@ -1551,7 +1551,27 @@ extension RunnerTests {
   }
 
   func pinch(app: XCUIApplication, scale: Double, x: Double?, y: Double?) -> RunnerInteractionOutcome {
+#if os(iOS)
+    // A coordinate tap+drag is a single-finger gesture: React Native reads it as a pan
+    // and the pinch scale never changes (#629). Drive the two-finger XCTest synthesis
+    // path (the same one transformGesture uses) with zero translation/rotation so RN's
+    // pinch recognizer actually fires.
+    let frame = interactionRoot(app: app).frame
+    let centerX = x ?? Double(frame.midX)
+    let centerY = y ?? Double(frame.midY)
+    return transformGesture(
+      app: app,
+      x: centerX,
+      y: centerY,
+      dx: 0,
+      dy: 0,
+      scale: scale,
+      degrees: 0,
+      durationMs: 300
+    )
+#else
     return performCoordinatePinch(app: app, scale: scale, x: x, y: y)
+#endif
   }
 
   func rotateGesture(app: XCUIApplication, degrees: Double, x: Double?, y: Double?, velocity: Double) -> RunnerInteractionOutcome {