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>

src/AcDream.UI.Abstractions/Panels/Chat/ChatInputParser.cs

@@ -304,4 +304,21 @@ public static class ChatInputParser
         foreach (var (v, _) in ChannelVerbs) set.Add(v);
         return set;
     }
+
+    /// <summary>
+    /// Returns true if <paramref name="verb"/> (with leading
+    /// <c>/</c>) is one this parser routes — used by callers that
+    /// need to distinguish "unknown slash command" from "known
+    /// verb with bad arguments" without reproducing the alias
+    /// tables. <c>@</c>-prefixed verbs need to be normalized to
+    /// <c>/</c> before passing.
+    /// </summary>
+    public static bool IsKnownVerb(string verb) => AllKnownVerbs.Contains(verb);
+
+    /// <summary>
+    /// Pull the first whitespace-separated token (the command verb)
+    /// from <paramref name="command"/>. Returns the entire string if
+    /// there is no whitespace.
+    /// </summary>
+    public static string GetVerbToken(string command) => ExtractVerb(command);
 }