fix(ios): guard against double touchesEnded delivery on iOS 26

[hggzm]

Problem

Action.ToggleVisibility fires twice on iOS 26, causing toggled content to open then immediately collapse.

iOS 26 introduced a new Gestures framework that re-delivers touchesEnded:withEvent: twice for the same physical tap:

1. Once through the normal UIKit dispatch path (AXPApplication.sendEvent:)
2. A second time via a deferred CoreFoundation run-loop callback

Critically, the second delivery uses a new UIEvent object (different pointer), so simple event pointer deduplication doesn't work.

In ACRContentStackView, touchesEnded:withEvent: calls doSelectAction unconditionally, so Action.ToggleVisibility fires twice per tap — opening the card then immediately closing it again.

Customer Impact

This blocks Fast Retailing's ServiceNow Now Assist rollout (100+ stores worldwide). Their card uses ColumnSet.selectAction with Action.ToggleVisibility to expand/collapse a "Sources" section. Microsoft support case: TrackingID# 2603110030008961.

Version Matrix (Customer-Reported)

iOS Version	Teams Version	Issue Occurs
26.3.1	8.3.1	YES
26.1	8.3.1	YES
17.7	8.3.1	NO
26.3.1	8.2.1	NO

Same card works on Android, Desktop, Web.

Fix

In ACRContentStackView.mm:

1. Added BOOL _hasFiredActionForCurrentTouch ivar
2. touchesBegan:withEvent: resets the flag to NO at the start of each new touch sequence
3. touchesEnded:withEvent: checks the flag before firing — skips on re-delivery, sets it to YES on first fire
4. Added touchesCancelled:withEvent: handler to reset the flag and forward the event

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
{
    _hasFiredActionForCurrentTouch = NO;
    // ... existing logic
}

- (void)touchesEnded:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
{
    if (self.selectActionTarget) {
        if (_hasFiredActionForCurrentTouch) { return; }
        _hasFiredActionForCurrentTouch = YES;
        [self.selectActionTarget doSelectAction];
    } else {
        [self.nextResponder touchesEnded:touches withEvent:event];
    }
}

Why This Fix Is Safe

• The guard is entirely local to the touch sequence lifecycle (touchesBegan → touchesEnded/touchesCancelled)
• It does not affect any other action types — only prevents duplicate delivery within the same touch
• touchesCancelled properly resets the flag to avoid stuck state
• No Teams app changes required — fix is confined to the AdaptiveCards SDK

How Verified

• iOS 26.2 simulator (Xcode 16.4, macos-15 GitHub Actions runner, com.apple.CoreSimulator.SimRuntime.iOS-26-2)
• Custom testToggleVisibilityDoubleFire UI test:
  • Navigates to Action.ToggleVisibility.json card
  • Taps toggle button, waits 2s
  • Result: Element count changed from 54 → 56 (content stayed expanded, no double-fire)
  • Taps again, waits 2s
  • Result: Element count returned to 54 (clean round-trip)
• All existing unit tests pass (SDK Build Gate: ✅, Agent Validation Gate: ✅)
• iOS Visual Regression: ✅ (no screenshot diffs)
• AXe A11y Pipeline: ✅