Fix build warnings: exclude README and fix unused variable

Package.swift

@@ -34,7 +34,8 @@ let package = Package(
                 "Assets.xcassets",
                 "bitchat.entitlements",
                 "bitchat-macOS.entitlements",
-                "LaunchScreen.storyboard"
+                "LaunchScreen.storyboard",
+                "ViewModels/Extensions/README.md"
             ],
             resources: [
                 .process("Localizable.xcstrings")

bitchatTests/ChatViewModelTests.swift

@@ -120,7 +120,7 @@ struct ChatViewModelReceivingTests {
 
     @Test @MainActor
     func didReceiveMessage_callsDelegate() async {
-        let (viewModel, transport) = makeTestableViewModel()
+        let (_, transport) = makeTestableViewModel()
 
         let message = BitchatMessage(
             id: "msg-001",