fix(healthchat): keep legacy accounts on the typed account provider

UnitTests/Sources/AuthenticationStartScreenViewModelTests.swift

@@ -225,6 +225,23 @@ final class AuthenticationStartScreenViewModelTests {
         #expect(account == classicAppAccount)
     }
     
+    @Test
+    func healthChatProviderAllowsLegacyAccount() async {
+        // Given the account providers HealthChat ships with and an account from the legacy HealthChat app.
+        let classicAppAccount = makeClassicAppAccount(serverName: "healthchat.ch",
+                                                      homeserverURL: "https://matrix.healthchat.ch")
+        appSettings = HealthChatAppSettingsHook().configure(appSettings)
+        await setupViewModel(classicAppAccount: classicAppAccount)
+        
+        // Then the legacy account must still be offered for migration. A silent failure here logs every
+        // updating user out of the migration path, so the real hook values are tested, not a stand-in.
+        guard case .welcomeBack(let account) = context.viewState.classicAppMode else {
+            Issue.record("Expected classicAppMode to be .welcomeBack")
+            return
+        }
+        #expect(account == classicAppAccount)
+    }
+    
     @Test
     func singleProviderWithDisallowedClassicAppAccount() async {
         // Given a view model for an app that only allows a single provider that does NOT match the Classic account's server.