feat(chat): Phase J Tier 1+2 - @ verb prefix, /retell, /framerate, /loc

Three-tier rollout per the 2026-04-25 retail @help dump showing the
full ACE command surface. Tier 1 + most of Tier 2 in one commit.

TIER 1 - @ as / equivalent

ACE accepts both / and @ as verb prefixes (per its own help text:
"Note: You may substitute a forward slash (/) for the at symbol
(@)."). ChatInputParser now normalises @ to / for the verb-match
phase and re-enters parsing. Critical: for verbs we don't recognise
(@acehelp, @tele, @die, @version, @loc-on-server, @nonsense, ...),
the original @ is kept in the message text so ACE's CommandManager
intercepts the message server-side. If we substituted / there too,
ACE would treat it as plain Talk and broadcast it.

Result: @a hi / @tell Bob hi / @help / @clear / @reply / @retell
all route exactly like their / counterparts. @acehelp / @tele /
@version / @die etc. pass through to the server intact.

TIER 2 - client-only commands

- /retell <msg> (also @retell): resend to the last person you
  tell'd. Mirrors retail @retell. ChatVM tracks
  LastOutgoingTellTarget on each OnSelfSent(Tell, ...) entry —
  SenderGuid==0 distinguishes outgoing echo from inbound whispers,
  same way LastIncomingTellSender already worked. ChatInputParser
  takes a new optional lastOutgoingTellTarget param.

- /framerate (also @framerate): prints "Framerate: 144.2 FPS"
  into chat. Wired via a new ChatVM.FpsProvider Func<float>
  callback set by GameWindow at construction (closes over
  _lastFps). Falls back to "(provider unavailable)" if no
  callback is wired (tests / pre-live).

- /loc (also @loc): prints "Location: (123.4, 567.8, 60.0)" into
  chat. Wired via ChatVM.PositionProvider Func<Vector3> closing
  over GetDebugPlayerPosition() in GameWindow. ACE has a server-
  side @loc too; client wins here (instantaneous + uses the local
  interpolated position).

ChatPanel.TryHandleClientCommand grew @ aliases for /help /clear
/framerate /loc and the new EqAny helper for case-insensitive
multi-string matching. Help text rewritten to reference the
/ <-> @ equivalence and point at @acehelp / @acecommands for ACE's
full command list.

TIER 3 - automatic (no code)

Most retail @-commands (@allegiance motd, @afk, @die, @lifestone,
@corpse, @marketplace, @pkarena, @emote/@emotes, @fillcomps,
@permit, @consent, @squelch, @unsquelch, @messagetypes, @age,
@birth, @day, @endurance, @pklite, @version, @filter, @unfilter,
@loadfile, @log, @marketplace, ...) are server-side ACE commands.
Tier 1's passthrough takes care of them automatically — they
arrive via Talk, ACE recognises the @ and intercepts, replies via
SystemChat (which our 0xF7E0 wiring renders as [System] lines).

DEFERRED

- @saveui / @loadui / @lockui: ImGui layout save/load, ~1 hr
  standalone task. Filed for follow-up.
- @title <text>: rename chat window. ImGui window-id complications.
- Toggle-style @framerate (FPS overlay on/off): print-once is
  simpler and matches retail's most-common usage.

30 new tests:
- ChatInputParserAtPrefixTests: 11 covering @-prefix recognition,
  unknown-@ passthrough, /retell and @retell.
- ChatVMRetellAndProvidersTests: 8 covering LastOutgoingTellTarget
  tracking, FpsProvider/PositionProvider callbacks, no-provider
  fallback.
- ChatPanelInputTests: +3 (/framerate, @loc, @acehelp passthrough).

Solution total: 1063 green (243 Core.Net + 160 UI + 660 Core),
0 warnings.

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

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

@@ -41,8 +41,10 @@ public sealed class ChatPanelInputTests
         Assert.Empty(bus.Published);
         var entry = Assert.Single(log.Snapshot());
         Assert.Equal(ChatKind.System, entry.Kind);
-        Assert.Contains("acdream chat commands:", entry.Text);
+        // Help text mentions / and @ equivalence and points at @acehelp
+        // for the server's full command list.
         Assert.Contains("/tell", entry.Text);
+        Assert.Contains("@acehelp", entry.Text);
     }
 
     [Theory]
@@ -67,6 +69,73 @@ public sealed class ChatPanelInputTests
         Assert.Single(log.Snapshot());
     }
 
+    [Fact]
+    public void Submit_FramerateCommand_PrintsFpsAndDoesNotPublish()
+    {
+        var log = new ChatLog();
+        var vm  = new ChatVM(log) { FpsProvider = () => 60f };
+        var panel = new ChatPanel(vm);
+        var bus = new RecordingBus();
+        var renderer = new FakePanelRenderer
+        {
+            InputTextSubmitNextSubmitted = "/framerate",
+            InputTextSubmitNextBufferAfter = "",
+        };
+
+        panel.Render(new PanelContext(0.016f, bus), renderer);
+
+        Assert.Empty(bus.Published);
+        var entry = Assert.Single(log.Snapshot());
+        Assert.Contains("60.0 FPS", entry.Text);
+    }
+
+    [Fact]
+    public void Submit_LocCommand_PrintsPositionAndDoesNotPublish()
+    {
+        var log = new ChatLog();
+        var vm  = new ChatVM(log)
+        {
+            PositionProvider = () => new System.Numerics.Vector3(10f, 20f, 30f),
+        };
+        var panel = new ChatPanel(vm);
+        var bus = new RecordingBus();
+        var renderer = new FakePanelRenderer
+        {
+            InputTextSubmitNextSubmitted = "@loc",
+            InputTextSubmitNextBufferAfter = "",
+        };
+
+        panel.Render(new PanelContext(0.016f, bus), renderer);
+
+        Assert.Empty(bus.Published);
+        var entry = Assert.Single(log.Snapshot());
+        Assert.Contains("(10.0, 20.0, 30.0)", entry.Text);
+    }
+
+    [Fact]
+    public void Submit_AtAcehelp_PassesThroughToSayWithAtIntact()
+    {
+        // Unknown @-verb falls through to the default channel with the
+        // literal "@acehelp" text intact so ACE's CommandManager
+        // intercepts it server-side. We DO publish a SendChatCmd here —
+        // the publish is what carries the message to the server.
+        var log = new ChatLog();
+        var vm  = new ChatVM(log);
+        var panel = new ChatPanel(vm);
+        var bus = new RecordingBus();
+        var renderer = new FakePanelRenderer
+        {
+            InputTextSubmitNextSubmitted = "@acehelp",
+            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("@acehelp", sendCmd.Text);
+    }
+
     [Fact]
     public void Submit_ClearCommand_DrainsLog_AndDoesNotPublish()
     {