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>

bitchatTests/ChatViewModelTests.swift

@@ -263,6 +263,59 @@ struct ChatViewModelCommandTests {
             #expect(transport.sentPrivateMessages.isEmpty)
         }
     }
+
+    @Test @MainActor
+    func handleCommand_outputRoutesToOpenPrivateChat() async {
+        let (viewModel, transport) = makeTestableViewModel()
+        let peerID = PeerID(str: "0000000000000002")
+        transport.simulateConnect(peerID, nickname: "Alice")
+        viewModel.selectedPrivateChatPeer = peerID
+
+        viewModel.handleCommand("/help")
+
+        #expect(viewModel.privateChats[peerID]?.last?.content == CommandProcessor.helpText)
+        #expect(!viewModel.messages.contains { $0.content == CommandProcessor.helpText })
+    }
+
+    @Test @MainActor
+    func handleCommand_errorRoutesToOpenPrivateChat() async {
+        let (viewModel, transport) = makeTestableViewModel()
+        let peerID = PeerID(str: "0000000000000002")
+        transport.simulateConnect(peerID, nickname: "Alice")
+        viewModel.selectedPrivateChatPeer = peerID
+
+        viewModel.handleCommand("/bogus")
+
+        let dmContents = viewModel.privateChats[peerID]?.map(\.content) ?? []
+        #expect(dmContents.contains { $0.hasPrefix("unknown command: /bogus") })
+        #expect(!viewModel.messages.contains { $0.content.hasPrefix("unknown command: /bogus") })
+    }
+
+    @Test @MainActor
+    func handleCommand_outputRoutesToPublicTimelineWithoutOpenDM() async {
+        let (viewModel, _) = makeTestableViewModel()
+
+        viewModel.handleCommand("/bogus")
+
+        #expect(viewModel.messages.last?.content.hasPrefix("unknown command: /bogus") == true)
+    }
+
+    @Test @MainActor
+    func handleCommand_msgSuccessLandsInNewlyOpenedChat() async {
+        let (viewModel, transport) = makeTestableViewModel()
+        let peerID = PeerID(str: "0000000000000002")
+        transport.simulateConnect(peerID, nickname: "Alice")
+        let resolved = await TestHelpers.waitUntil({
+            viewModel.getPeerIDForNickname("Alice") == peerID
+        }, timeout: TestConstants.defaultTimeout)
+        #expect(resolved)
+
+        viewModel.handleCommand("/msg Alice")
+
+        #expect(viewModel.selectedPrivateChatPeer == peerID)
+        #expect(viewModel.privateChats[peerID]?.last?.content == "started private chat with Alice")
+        #expect(!viewModel.messages.contains { $0.content == "started private chat with Alice" })
+    }
 }
 
 // MARK: - Composer Tests