fix(chat): / and @ are equivalent command prefixes (retail parity)

Retail treats / and @ interchangeably for commands, but two client-side
layers broke the / spelling for server commands:

- ChatCommandRouter refused ANY unknown /verb with a local "Unknown
  command" guess — so /tele, /ci, /acehelp never reached ACE even
  though ACE supports them. The guard is gone; the server is now the
  single authority on what's a valid command (ACE replies "Unknown
  command: x" itself).
- ChatInputParser passed unknown /verbs through as literal speech.
  ACE's GameActionTalk only intercepts the @ form on the wire (the /
  acceptance in CommandManager is the server CONSOLE path), so the
  parser now rewrites unknown /xyz -> @xyz.

Both command pass-throughs (@ and rewritten /) now also force the Say
channel: GameActionTalk (0x0015) is the only wire action ACE parses
commands on — previously a command typed with a chat channel active
would broadcast as channel speech.

Phase J Tier 4 ("/-text must never broadcast as speech") still holds:
letter-verbed input goes out as an @command (never speech), and
command-shaped-but-verbless input ("/", "//shrug") is refused locally
by a narrow router guard.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/AcDream.UI.Abstractions.Tests/Panels/Chat/ChatCommandRouterTests.cs

@@ -54,13 +54,31 @@ public class ChatCommandRouterTests
     }
 
     [Fact]
-    public void UnknownSlashVerb_ShowsSystemMessage_DoesNotPublish()
+    public void UnknownSlashVerb_RoutesToServerInAtForm()
     {
+        // Retail / ≡ @: unknown verbs are the server's to judge. The
+        // parser rewrites /-form to @-form (ACE's GameActionTalk only
+        // intercepts @ on the wire); ACE answers "Unknown command: x"
+        // for verbs it doesn't know — no local guess.
         var (vm, log, bus) = Fixture();
         var outcome = ChatCommandRouter.Submit("/notacommand", vm, bus, ChatChannelKind.Say);
-        Assert.Equal(SubmitOutcome.UnknownCommand, outcome);
-        Assert.Null(bus.Last);
-        Assert.Contains(log.Snapshot(), e => e.Text.Contains("Unknown command"));
+        Assert.Equal(SubmitOutcome.Sent, outcome);
+        Assert.NotNull(bus.Last);
+        Assert.Equal("@notacommand", bus.Last!.Text);
+        Assert.DoesNotContain(log.Snapshot(), e => e.Text.Contains("Unknown command"));
+    }
+
+    [Fact]
+    public void ServerCommandWithArgs_PublishesAtFormAsSay_EvenOnChannelDefault()
+    {
+        // Commands resolve before channel routing (retail behavior):
+        // even with Fellowship as the active input channel, a command
+        // goes out as Say/Talk — the only wire action ACE parses @ on.
+        var (vm, _, bus) = Fixture();
+        var outcome = ChatCommandRouter.Submit("/ci 629 5", vm, bus, ChatChannelKind.Fellowship);
+        Assert.Equal(SubmitOutcome.Sent, outcome);
+        Assert.Equal(ChatChannelKind.Say, bus.Last!.Channel);
+        Assert.Equal("@ci 629 5", bus.Last.Text);
     }
 
     [Fact]