feat(services): add TellRouterService stub

Skeleton for the upcoming auto-open routing. Subscribes to
ChatGui.ChatMessageUnhandled and Dispose unsubscribes — when the routing
logic lands, it drops into OnChatMessage without touching the DI graph or
Plugin.cs registration.

HellionChat/Services/TellRouterService.cs

@@ -0,0 +1,32 @@
+using Dalamud.Game.Chat;
+using Dalamud.Plugin.Services;
+using Microsoft.Extensions.Logging;
+
+namespace HellionChat.Services;
+
+// Skeleton for the upcoming auto-open routing layer. Subscribes to IChatGui
+// up front so the DI graph and Plugin.cs registration stay frozen — when
+// the routing logic lands, it drops into OnChatMessage without touching
+// anything else.
+internal sealed class TellRouterService : IDisposable
+{
+    private readonly IChatGui _chatGui;
+    private readonly ILogger<TellRouterService> _logger;
+
+    public TellRouterService(IChatGui chatGui, ILogger<TellRouterService> logger)
+    {
+        _chatGui = chatGui;
+        _logger = logger;
+        _chatGui.ChatMessageUnhandled += OnChatMessage;
+    }
+
+    public void Dispose()
+    {
+        _chatGui.ChatMessageUnhandled -= OnChatMessage;
+    }
+
+    private void OnChatMessage(IChatMessage message)
+    {
+        // Intentional no-op until the routing implementation lands.
+    }
+}