feat: improve React Native support with new locators and assertions

[krismuhi]

Summary

• React Native role mapping — adds ReactTextView, ReactEditText, ReactImageView, ReactScrollView to ROLE_TYPE_MAP so getByRole('text'), getByRole('textfield'), getByRole('image'), getByRole('list') work on Android RN apps. ReactViewGroup maps to button only when clickable="true" or accessible="true" to avoid false positives.
• Full resource-id matching — stores resourceId on ViewNode so getByTestId('com.example:id/login_button') works alongside the existing short form getByTestId('login_button'). Useful for Appium migration.
• getByPlaceholder() locator — new locator strategy for matching elements by placeholder text (Android hint, iOS placeholderValue). Supports exact and substring matching.
• New assertions — toBeDisabled(), toBeSelected(), toHaveFocus(), toBeChecked(), toHaveValue() with full .not negation and auto-retry support.
• New Locator queries — isSelected(), isFocused(), isChecked(), getValue().
• isChecked on ViewNode — populated from Android checkable/checked attributes.
• Framework support table in README showing what works out of the box.

Test plan

• All 77 existing + new unit tests pass
• Verify role mapping against a real React Native app on Android
• Verify getByPlaceholder on both iOS and Android
• Review framework support table for accuracy