fix: avoid unsafe iOS keyboard dismissal - #957

Summary

Closes #952.

• Removes the iOS keyboard dismissal swipe/coordinate fallbacks that could type into focused fields on iOS 26.
• Keeps dismissal limited to safe native controls and updates the unsupported-operation copy/docs/help to match.

The dismiss-control search intentionally checks matching buttons beyond app.toolbars.buttons because iOS 26 may expose keyboard-accessory Done controls outside a UIToolbar. It remains bounded by exact safe labels and keyboard-accessory geometry, so it can tap a nearby dismiss control without falling back to input-mutating gestures or raw coordinates.

Touched files: 8. Scope stayed within iOS runner keyboard behavior plus related help/docs/tests.

Validation

• Verified in Safari on iPhone 17 Pro simulator: keyboard dismiss no longer appended TV to abc; it failed closed when no safe control was available.
• Verified in examples/test-app Checkout form on iPhone 17 Pro simulator: field stayed Final952 after keyboard dismiss returned UNSUPPORTED_OPERATION.
• Verified tvOS simulator path still reports keyboard unsupported.
• pnpm build
• pnpm build:xcuitest
• pnpm build:xcuitest:tvos
• pnpm exec vitest run src/utils/tests/args.test.ts src/commands/system/index.test.ts src/core/tests/dispatch-keyboard.test.ts src/core/tests/capabilities.test.ts
• pnpm exec vitest run src/platforms/ios/tests/runner-client.test.ts
• pnpm format
• pnpm check:quick