Route command output to the conversation where the command was typed (#1363)

CommandProcessor results (/help text, errors like "unknown command",
/msg confirmations) were always appended to the public timeline via
addSystemMessage, so a command typed inside a DM appeared to do
nothing until the user switched back to the public channel.

handleCommand now routes .success/.error output to the open private
chat when one is selected, falling back to the public timeline
otherwise. The DM selection is read after processing so commands that
switch chats (/msg) print into the conversation they just opened.

Follow-up to #1354, which added /help and surfaced this routing gap.

Co-authored-by: jack <jackjackbits@users.noreply.github.com>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

bitchat/ViewModels/ChatViewModel.swift

@@ -1435,7 +1435,7 @@ final class ChatViewModel: ObservableObject, BitchatDelegate, TransportEventDele
 
     /// Processes IRC-style commands starting with '/'.
     /// - Parameter command: The full command string including the leading slash
-    /// - Note: Supports commands like /nick, /msg, /who, /slap, /clear, /help
+    /// - Note: Supports commands like /msg, /who, /slap, /clear, /help
     @MainActor
     func handleCommand(_ command: String) {
         let result = commandProcessor.process(command)
@@ -1443,16 +1443,29 @@ final class ChatViewModel: ObservableObject, BitchatDelegate, TransportEventDele
         switch result {
         case .success(let message):
             if let msg = message {
-                addSystemMessage(msg)
+                addCommandOutput(msg)
             }
         case .error(let message):
-            addSystemMessage(message)
+            addCommandOutput(message)
         case .handled:
             // Command was handled, no message needed
             break
         }
     }
 
+    /// Command output belongs in the conversation where the user typed the
+    /// command; the public timeline is invisible while a DM is open. The DM
+    /// selection is read *after* processing so commands that switch chats
+    /// (`/msg`) print into the conversation they just opened.
+    @MainActor
+    private func addCommandOutput(_ content: String) {
+        if let peerID = selectedPrivateChatPeer {
+            addLocalPrivateSystemMessage(content, to: peerID)
+        } else {
+            addSystemMessage(content)
+        }
+    }
+
     // MARK: - Message Reception
 
     @MainActor