fix(chat): block / unknown commands from broadcasting as speech

User reported typing /ls (a command-style request, not chat) gets
echoed by the server as "You say, \"/ls\"". Slash-prefix is a
COMMAND surface, never a chat surface. Filed after the same flow
that produced @help and the welcome-message work.

Behavior change at the ChatPanel submit layer:
- Any /-prefixed input whose verb isn't in our alias tables now
  renders a local "[System] Unknown command: /foo. Type /help for
  the list." line and is NEVER published to the bus. No SendChatCmd,
  no Talk packet. The server never sees /foo.
- Known /-verbs (/say /tell /reply /retell /general /allegiance
  /patron /vassals /monarch /covassals /fellowship /lookingforgroup
  /trade /roleplay /society /olthoi /help /clear /framerate /loc
  and friends) still flow through ChatInputParser.Parse → SendChatCmd
  exactly as before.
- @-prefix unchanged: ACE's CommandManager handles unknown @ verbs
  server-side and replies via SystemChat ("Unknown command: foo")
  per ACE GameActionTalk.cs:21. Our @ -> / normalization for known
  verbs (Phase J Tier 1) and the @-passthrough fallthrough for
  unknown verbs both still apply.

ChatInputParser now exposes:
- IsKnownVerb(string verb): query against the union of every alias
  table. Used by ChatPanel to discriminate "unknown verb" from
  "known verb with bad args".
- GetVerbToken(string command): public alias of the existing
  ExtractVerb so callers can pull the first whitespace token without
  reproducing the helper.

Parse itself is unchanged — its existing fall-through (Say with
literal text) still applies for unknown /-verbs called directly via
the parser, but ChatPanel intercepts before reaching that path so
the fall-through never fires through the live submit pipeline. Tests
that directly call Parse continue to pass; the new ChatPanel-level
tests pin the unknown-command rejection.

19 new tests:
- ChatInputParserTests: 10 IsKnownVerb Theory cases + 4 GetVerbToken
  Theory cases.
- ChatPanelInputTests: 5 Theory cases for Submit_UnknownSlashCommand
  covering /foo, /ls, /mp <path>, /genio, and bare /.

Solution total: 1086 green (243 Core.Net + 183 UI + 660 Core),
0 warnings.

Acceptance: type /ls, /mp /path, /anything-not-known — see local
"[System] Unknown command: /xxx. Type /help for the list of
supported commands." Nothing reaches the wire.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

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

@@ -112,6 +112,38 @@ public sealed class ChatPanelInputTests
         Assert.Contains("(10.0, 20.0, 30.0)", entry.Text);
     }
 
+    [Theory]
+    [InlineData("/foo")]
+    [InlineData("/ls")]
+    [InlineData("/mp /tools/script.py")]
+    [InlineData("/genio public")]
+    [InlineData("/")]
+    public void Submit_UnknownSlashCommand_ShowsUnknownAndDoesNotPublish(string raw)
+    {
+        // 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.
+        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);
+
+        Assert.Empty(bus.Published);
+        var entry = Assert.Single(log.Snapshot());
+        Assert.Equal(ChatKind.System, entry.Kind);
+        Assert.Contains("Unknown command", entry.Text);
+        Assert.Contains("/help", entry.Text);
+    }
+
     [Fact]
     public void Submit_AtAcehelp_PassesThroughToSayWithAtIntact()
     {