feat(chat): Phase J - welcome message + own-echo dedup + long-form slash aliases + WeenieError templates

Six fixes from the 2026-04-25 live verify session.

1. ServerMessage (0xF7E0) wired to ChatLog. ACE's
   GameMessageSystemChat - used for the login banner "Welcome to
   Asheron's Call ... powered by ACEmulator ... type @acehelp" plus
   any future server broadcast - rides opcode 0xF7E0. The parser
   shipped in I.5 but the WorldSession.ServerMessageReceived event
   was never subscribed by GameWindow, so the welcome line was
   silently dropped. Subscribed now; same wave wires the missing
   EmoteHeard / SoulEmoteHeard / PlayerKilledReceived events that
   I.5 also left orphan.

2. Drop optimistic /say echo + plumb local-player-guid into ChatLog.
   ACE's HandleActionTalk broadcasts a HearSpeech back to the sender
   too, so we were double-printing every /say (own optimistic +
   server echo). New ChatLog.SetLocalPlayerGuid() pushes the chosen
   character guid in (mirrors VitalsVM pattern); OnLocalSpeech
   detects own-guid match and substitutes Sender="" so the formatter
   's IsOwnSpeaker path renders "You say, ..." instead of
   "+Acdream says, ...". Single line per /say.

3. IsOwnSpeaker check now applies to ChatKind.Channel too. Empty/
   "You" sender -> "[Allegiance] You say, \"text\"" instead of the
   "[Allegiance]  says, \"text\"" double-space hole that Phase I.6's
   OnSelfSent left when echoing legacy ChatChannel sends.

4. Long-form slash aliases: /general /allegiance /patron /vassals
   /monarch /covassals /fellowship /fellow /lookingforgroup
   /roleplay /rp /tr /gen, plus /s as alias for /say. Retail muscle
   memory expected these; the prior parser only recognized /g /a /p
   /v /m /cv /lfg /role and friends, so "/patron hello" fell
   through as /say with the literal "/patron" prefix.

5. WeenieError templates filled in for the codes the user hit:
   - 0x0414 YouAreNotInAllegiance  -> "You are not in an allegiance!"
   - 0x050F YouDoNotBelongToAFellowship -> "You do not belong to a Fellowship."
   Replaces the cryptic "WeenieError 0x0414" / "0x050F" lines.

6. @ command pass-through: ACE handles @help / @acehelp / @tele etc.
   server-side by intercepting Talk text with @ prefix; the user's
   message isn't broadcast and ACE replies via SystemChat. Drop the
   optimistic /say echo so the chat shows only the server's response
   (the SystemChat wiring from #1 surfaces it as [System] {help}).

Tests:
- 11 long-form-alias Theory cases on ChatInputParser.
- 3 own-guid-substitution cases on ChatLog (own match, different
  guid, pre-login fallback).
- Existing PrefixSubstring test refactored to "/genio" since the
  previous "/general" stub is now a real verb.

Solution total: 1021 green (243 Core.Net + 125 UI + 653 Core),
0 warnings, 0 errors. +14 tests.

Acceptance: at login, [System] Welcome to Asheron's Call appears.
Single "You say, \"hi\"" per /say. /allegiance with no allegiance
shows [Allegiance] You say, ... + [System] You are not in an
allegiance!. /patron / /vassals / /monarch route correctly.

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

tests/AcDream.Core.Tests/Chat/ChatLogLocalGuidTests.cs

@@ -0,0 +1,56 @@
+using AcDream.Core.Chat;
+
+namespace AcDream.Core.Tests.Chat;
+
+/// <summary>
+/// Phase J: <see cref="ChatLog.SetLocalPlayerGuid"/> teaches the log
+/// to recognize ACE's HearSpeech echo of the local player's own /say
+/// — the server broadcasts to all in range INCLUDING the sender, so
+/// we'd otherwise see both our optimistic "You say" and the
+/// third-person "+Acdream says" from the server. Substituting the
+/// sender to "" routes through the formatter's IsOwnSpeaker path so
+/// only the singular first-person line shows.
+/// </summary>
+public sealed class ChatLogLocalGuidTests
+{
+    [Fact]
+    public void OnLocalSpeech_OwnGuidMatch_SubstitutesYou()
+    {
+        var log = new ChatLog();
+        log.SetLocalPlayerGuid(0x5000_000A);
+
+        log.OnLocalSpeech("+Acdream", "hello world",
+            senderGuid: 0x5000_000A, isRanged: false);
+
+        var entry = log.Snapshot()[0];
+        Assert.Equal(ChatKind.LocalSpeech, entry.Kind);
+        Assert.Equal("You", entry.Sender);
+        Assert.Equal("hello world", entry.Text);
+    }
+
+    [Fact]
+    public void OnLocalSpeech_DifferentGuid_KeepsSenderName()
+    {
+        var log = new ChatLog();
+        log.SetLocalPlayerGuid(0x5000_000A);
+
+        log.OnLocalSpeech("Caith", "hi",
+            senderGuid: 0x5000_0042, isRanged: false);
+
+        Assert.Equal("Caith", log.Snapshot()[0].Sender);
+    }
+
+    [Fact]
+    public void OnLocalSpeech_NoLocalGuidSet_FallsBackToEmptySubstitution()
+    {
+        // Pre-login (guid not yet known), the existing empty-sender
+        // substitution still applies — server-driven ranged echoes
+        // arrive with sender="" before the player has a guid.
+        var log = new ChatLog();
+        log.OnLocalSpeech("", "anyone home?",
+            senderGuid: 0u, isRanged: true);
+
+        Assert.Equal("You", log.Snapshot()[0].Sender);
+        Assert.Equal(ChatKind.RangedSpeech, log.Snapshot()[0].Kind);
+    }
+}