skill: add Android skills

.agents/skills/verified-email/references/android/identity/sign-in/credential-manager-webview.md

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+This document describes how to integrate the Credential Manager API with an
+Android app that uses WebView. Credential Manager is supported natively in the
+`android.webkit.WebView` library in [version 1.12.0](https://developer.android.com/jetpack/androidx/releases/webkit#1.12.0) and later.
+
+## Prerequisites
+
+To use Credential Manager in WebView, add the following dependencies to your app
+module's build script:
+
+    dependencies {
+      implementation("androidx.credentials:credentials:1.6.0-beta02")   
+      implementation("androidx.credentials:credentials-play-services-auth:1.6.0-beta02")
+      implementation("androidx.webkit:webkit:1.14.0")
+    }
+
+You will also need to associate your app with a website that your app owns using
+digital asset linking. For more information, see
+[adding digital asset linking](https://developer.android.com/identity/credential-manager/prerequisites).
+
+## Use the WebKit library
+
+To use the WebKit library, check for feature support, and then enable support by
+calling `setWebAuthenticationSupport()`:
+
+    class WebViewActivity : ComponentActivity() {
+        override fun onCreate(savedInstanceState: Bundle?) {
+            super.onCreate(savedInstanceState)
+            setContent {
+                // Put your webview link here.
+                val url = "https://project-sesame-426206.appspot.com/passkey-signup"
+                AndroidView(
+                    factory = { context ->
+                        WebView(context).apply {
+                            settings.javaScriptEnabled = true
+
+                            webViewClient = WebViewClientImpl()
+                        }
+                    },
+                    update = { webView ->
+                        run {
+                            webView.loadUrl(url)
+                            if (WebViewFeature.isFeatureSupported(WebViewFeature.WEB_AUTHENTICATION)) {
+                                WebSettingsCompat.setWebAuthenticationSupport(
+                                    webView.settings,
+                                    WebSettingsCompat.WEB_AUTHENTICATION_SUPPORT_FOR_APP,
+                                )
+                                // Check if getWebauthenticationSupport may have been disabled by the WebView.
+                                Log.e(
+                                    "WebViewPasskeyDemo",
+                                    "getWebAuthenticationSupport result: " + WebSettingsCompat.getWebAuthenticationSupport(
+                                        webView.settings
+                                    ),
+                                )
+                            } else {
+                                Log.e("WebViewPasskeyDemo", "WebView does not support passkeys.")
+                            }
+                        }
+                    },
+                )
+            }
+        }
+    }
+
+> [!NOTE]
+> **Note:** The WebKit library doesn't support `mediation:"conditional"` requests.
+
+## Web integration
+
+To learn how to build Web integration see
+[Create a passkey for passwordless logins](https://web.dev/passkey-registration/).
+You can also reference the [demo site source](https://github.com/deephand/webauthn-in-webview).
+
+## Testing and deployment
+
+Test the entire flow thoroughly in a controlled environment to verify proper
+communication between the Android app, the web page, and the backend.
+
+Deploy the integrated solution to production, verifying that the backend can
+handle incoming registration and authentication requests. The backend code
+should generate initial JSON for registration (create) and authentication (get)
+processes. It should also handle validation and verification of the responses
+received from the web page.
+
+Verify the implementation corresponds to the [UX recommendations](https://developer.android.com/design/ui/mobile/guides/patterns/passkeys).