feat(ios): hoist DebugBridgeTouch into canonical templates

Bridges.swift.template imports DebugBridgeTouch but no .m/.h template
shipped — consuming apps installing the canonical drop-in would hit a
linker error. Closes that gap with the fixture's verified working code.

Changes:

- New ios-qa/templates/DebugBridgeTouch.{h,m}.template files (carbon
  copies of the fixture sources, including the iOS-18+ SwiftUI hit-test
  fix verified on iPhone 17 Pro Max).
- Package.swift.template splits into 3 product targets: DebugBridgeCore
  (Swift, cross-platform), DebugBridgeUI (Swift, iOS-only), DebugBridgeTouch
  (Obj-C, iOS-only). Consuming app adds one dependency on DebugBridgeUI;
  Core + Touch come in transitively.
- DebugBridgeTouch sources wrap their body in #if TARGET_OS_IOS so the
  cross-platform `swift build` on macOS host doesn't choke on UIKit. On
  iOS the real implementation is active; on macOS sendTapAtPoint: is a
  no-op returning NO.
- New parity tests pin template ↔ fixture content so future fixture
  fixes propagate or fail loudly.
- Restrict swift-build host tests to DebugBridgeCore (the only target
  buildable on macOS) and bring up the previously broken XCTest run via
  --filter.

Verified post-change: real iPhone 17 Pro Max, iOS 26.5, three /tap
requests against the rebuilt app — counter went 0 → 3, SwiftUI Button
onTap fires every time. Templates now sufficient to ship to any
consuming iOS app.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

test/fixtures/ios-qa/FixtureApp/Sources/DebugBridgeTouch/DebugBridgeTouch.m

@@ -18,6 +18,10 @@
 //    IOHIDEventSetIntegerValue, IOHIDEventAppendEvent.
 
 #import "DebugBridgeTouch.h"
+#import <TargetConditionals.h>
+
+#if TARGET_OS_IOS
+
 #import <UIKit/UIKit.h>
 #import <objc/runtime.h>
 #import <objc/message.h>
@@ -281,3 +285,17 @@ static id DBT_HitTestView(UIWindow *window, CGPoint point) {
 }
 
 @end
+
+#else // !TARGET_OS_IOS
+
+// macOS / Catalyst / other non-iOS host build: no-op stub so the module
+// resolves cleanly without UIKit or IOKit. The Swift cross-platform tests
+// don't exercise touch synthesis; that's iOS-only by definition.
+@implementation DebugBridgeTouch
++ (BOOL)sendTapAtPoint:(CGPoint)point inWindow:(UIWindow *)window {
+    (void)point; (void)window;
+    return NO;
+}
+@end
+
+#endif // TARGET_OS_IOS