Suppress SignerActivity UI when the request is handled by a bunker proxy

Bunker proxy accounts forward every signing request to the remote
bunker and call finishAndRemoveTask() once the response is delivered.
Until now, SignerActivity still rendered its biometric prompt and
approval bottom sheet while the forward was in flight, so the user saw
a UI flash even though the work happens entirely in the background.

Now, in both onCreate and onNewIntent, if the intent's target account
is a proxy, set a transparent window background and skip setContent.
The proxy still runs in IntentUtils.handleProxyIntent and finishes the
activity itself once the bunker responds.

app/src/main/java/com/greenart7c3/nostrsigner/SignerActivity.kt

@@ -68,7 +68,20 @@ class SignerActivity : AppCompatActivity() {
 
         Amber.instance.setMainActivity(this)
         mainViewModel = MainViewModel(applicationContext)
+
+        // If the request will be served by a bunker proxy account, the proxy
+        // forwards it transparently and finishes the activity itself. Render
+        // nothing so the user does not see the approval bottom sheet flash.
+        val isProxyHandled = isProxyHandledIntent(intent)
+
         intent?.let { mainViewModel.onNewIntent(it, callingPackage) }
+
+        if (isProxyHandled) {
+            window.setBackgroundDrawable(android.graphics.drawable.ColorDrawable(android.graphics.Color.TRANSPARENT))
+            setContent { }
+            return
+        }
+
         setContent {
             NostrSignerTheme {
                 HttpClientManager.setDefaultUserAgent("Amber/${BuildConfig.VERSION_NAME}")
@@ -221,6 +234,11 @@ class SignerActivity : AppCompatActivity() {
         super.onNewIntent(intent)
         setIntent(intent)
         if (::mainViewModel.isInitialized) {
+            // Mirror the onCreate gate: if a proxy account will silently
+            // forward this intent, we never want to surface the approval UI.
+            if (isProxyHandledIntent(intent)) {
+                window.setBackgroundDrawable(android.graphics.drawable.ColorDrawable(android.graphics.Color.TRANSPARENT))
+            }
             mainViewModel.onNewIntent(intent, callingPackage)
         }
     }
@@ -239,6 +257,21 @@ class SignerActivity : AppCompatActivity() {
         super.onDestroy()
     }
 
+    /**
+     * Returns true if the current intent will be handled silently by the bunker
+     * proxy. In that case the activity should not render its approval UI — the
+     * proxy forwards the request to the remote bunker and calls
+     * [finishAndRemoveTask] from [IntentUtils.handleProxyIntent].
+     */
+    private fun isProxyHandledIntent(intent: Intent?): Boolean {
+        if (intent == null) return false
+        if (intent.action != Intent.ACTION_VIEW && intent.data == null) return false
+        val userFromIntent = intent.getStringExtra("current_user")
+        val npub = mainViewModel.getAccount(userFromIntent) ?: return false
+        val account = LocalPreferences.loadFromEncryptedStorageSync(applicationContext, npub) ?: return false
+        return account.isProxy
+    }
+
     private fun rejectIfRateLimited(intent: Intent?): Boolean {
         if (intent == null) return false
         val key = IntentRateLimitInspector.inspect(intent, callingPackage) ?: return false