Fix build: remove unnecessary WryWebViewPanel casts after alpha-13 bump

[Copilot]

In composewebview alpha-13, nativeWebView now has WryWebViewPanel as its declared return type, making the explicit as? WryWebViewPanel casts redundant. With -Werror set, the resulting "No cast needed" warnings failed the build.

Changes

• WebViewLoginScreen.kt: Remove as? WryWebViewPanel casts on nativeWebView accesses and drop the now-unused import

// Before
(state.webView?.nativeWebView as? WryWebViewPanel)?.clearAllCookies()
(state.webView?.nativeWebView as? WryWebViewPanel)?.getCookiesForUrl(actualUrl).orEmpty()

// After
state.webView?.nativeWebView?.clearAllCookies()
state.webView?.nativeWebView?.getCookiesForUrl(actualUrl).orEmpty()

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