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/ChatPanelInputTests.cs

@@ -113,18 +113,43 @@ public sealed class ChatPanelInputTests
     }
 
     [Theory]
-    [InlineData("/foo")]
-    [InlineData("/ls")]
-    [InlineData("/mp /tools/script.py")]
-    [InlineData("/genio public")]
-    [InlineData("/")]
-    public void Submit_UnknownSlashCommand_ShowsUnknownAndDoesNotPublish(string raw)
+    [InlineData("/foo",                 "@foo")]
+    [InlineData("/ls",                  "@ls")]
+    [InlineData("/mp /tools/script.py", "@mp /tools/script.py")]
+    [InlineData("/genio public",        "@genio public")]
+    public void Submit_UnknownSlashCommand_RoutesToServerAsAtCommand(string raw, string expectedText)
     {
-        // Phase J Tier 4: /-prefixed text is NEVER broadcast as plain
-        // speech. Filed after a 2026-04-25 trace where typing /ls (a
-        // command-style request the user wanted) was getting echoed by
-        // the server as "You say, \"/ls\"". Now we intercept and show
-        // a local "Unknown command" line; nothing goes on the wire.
+        // Phase J Tier 4 held: /-prefixed text is still NEVER broadcast
+        // as plain speech. Retail treats / and @ as equivalent command
+        // prefixes, so unknown verbs now go to the SERVER as @commands
+        // (ACE's GameActionTalk intercepts @ on the Say action and
+        // answers "Unknown command: x" itself) instead of a local guess.
+        var log = new ChatLog();
+        var vm  = new ChatVM(log);
+        var panel = new ChatPanel(vm);
+        var bus = new RecordingBus();
+        var renderer = new FakePanelRenderer
+        {
+            InputTextSubmitNextSubmitted = raw,
+            InputTextSubmitNextBufferAfter = "",
+        };
+
+        panel.Render(new PanelContext(0.016f, bus), renderer);
+
+        var sendCmd = Assert.IsType<SendChatCmd>(Assert.Single(bus.Published));
+        Assert.Equal(ChatChannelKind.Say, sendCmd.Channel);
+        Assert.Equal(expectedText, sendCmd.Text);
+        Assert.Empty(log.Snapshot());   // no local "Unknown command" guess
+    }
+
+    [Theory]
+    [InlineData("/")]
+    [InlineData("//shrug")]
+    public void Submit_CommandShapedWithoutVerb_ShowsUnknownAndDoesNotPublish(string raw)
+    {
+        // Command-shaped but no letter verb: refused locally — this is
+        // the remaining Tier-4 guard (never broadcast /-text as speech,
+        // and don't put junk @-rewrites on the wire either).
         var log = new ChatLog();
         var vm  = new ChatVM(log);
         var panel = new ChatPanel(vm);