feat(net): SocialActions — query / fellowship / channel / options outbound

Broad batch of GameActions for features the UI will wire to buttons +
hotkeys: /hp query, ping keepalive, fellowship full lifecycle,
character-options persist, chat channel subscribe/unsubscribe.

Wire layer:
- QueryHealth (0x01BF): u32 targetGuid — server replies UpdateHealth
  (0x01C0, already parsed by Phase F.1 dispatcher + routed to
  CombatState).
- PingRequest (0x01E9): u32 clientId — server echoes PingResponse
  (0x01EA) with matching id. Keepalive use.
- FellowshipCreate (0x00A2): string16L name + 2 u8 bools.
- FellowshipQuit (0x00A3): u8 disband.
- FellowshipDismiss (0x00A4) / FellowshipRecruit (0x00A5): u32 guid.
- FellowshipUpdate (0x00A6): u8 open.
- SetCharacterOptions (0x01A1): u32 options bitmap.
- AddChannel (0x0145) / RemoveChannel (0x0146): string16L channelName.

Tests (10 new): byte-exact wire encoding for each action.

Build green, 182 Core.Net tests pass (up from 172).

Ref: r08 §3 rows 0x01BF / 0x01E9 / 0x00A2-0x00A6 / 0x01A1 / 0x0145 / 0x0146.

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

tests/AcDream.Core.Net.Tests/Messages/SocialActionsTests.cs

@@ -0,0 +1,111 @@
+using System;
+using System.Buffers.Binary;
+using System.Text;
+using AcDream.Core.Net.Messages;
+using Xunit;
+
+namespace AcDream.Core.Net.Tests.Messages;
+
+public sealed class SocialActionsTests
+{
+    [Fact]
+    public void BuildQueryHealth_HasOpcode0x01BFAndGuid()
+    {
+        byte[] body = SocialActions.BuildQueryHealth(seq: 3, targetGuid: 0xCAFE);
+        Assert.Equal(SocialActions.QueryHealthOpcode,
+            BinaryPrimitives.ReadUInt32LittleEndian(body.AsSpan(8)));
+        Assert.Equal(0xCAFEu,
+            BinaryPrimitives.ReadUInt32LittleEndian(body.AsSpan(12)));
+    }
+
+    [Fact]
+    public void BuildPingRequest_HasOpcode0x01E9()
+    {
+        byte[] body = SocialActions.BuildPingRequest(seq: 1, clientId: 42);
+        Assert.Equal(SocialActions.PingRequestOpcode,
+            BinaryPrimitives.ReadUInt32LittleEndian(body.AsSpan(8)));
+        Assert.Equal(42u,
+            BinaryPrimitives.ReadUInt32LittleEndian(body.AsSpan(12)));
+    }
+
+    [Fact]
+    public void BuildFellowshipCreate_StringThenBools()
+    {
+        byte[] body = SocialActions.BuildFellowshipCreate(
+            seq: 1, fellowshipName: "Team", openness: true, shareXp: false);
+
+        Assert.Equal(SocialActions.FellowshipCreateOpcode,
+            BinaryPrimitives.ReadUInt32LittleEndian(body.AsSpan(8)));
+        // String at offset 12: u16 length = 4
+        ushort len = BinaryPrimitives.ReadUInt16LittleEndian(body.AsSpan(12));
+        Assert.Equal(4, len);
+        Assert.Equal("Team", Encoding.ASCII.GetString(body.AsSpan(14, 4)));
+        // string16L record = 2+4=6, pad 2 → advance by 8.
+        // Then 2 bools at offset 20,21.
+        Assert.Equal(1, body[20]);  // openness true
+        Assert.Equal(0, body[21]);  // shareXp false
+    }
+
+    [Fact]
+    public void BuildFellowshipQuit_CarriesDisbandFlag()
+    {
+        byte[] body = SocialActions.BuildFellowshipQuit(seq: 1, disband: true);
+        Assert.Equal(SocialActions.FellowshipQuitOpcode,
+            BinaryPrimitives.ReadUInt32LittleEndian(body.AsSpan(8)));
+        Assert.Equal(1, body[12]);
+    }
+
+    [Fact]
+    public void BuildFellowshipDismiss_HasGuid()
+    {
+        byte[] body = SocialActions.BuildFellowshipDismiss(seq: 1, targetGuid: 0xDEAD);
+        Assert.Equal(SocialActions.FellowshipDismissOpcode,
+            BinaryPrimitives.ReadUInt32LittleEndian(body.AsSpan(8)));
+        Assert.Equal(0xDEADu,
+            BinaryPrimitives.ReadUInt32LittleEndian(body.AsSpan(12)));
+    }
+
+    [Fact]
+    public void BuildFellowshipRecruit_HasGuid()
+    {
+        byte[] body = SocialActions.BuildFellowshipRecruit(seq: 1, targetGuid: 0xBEEF);
+        Assert.Equal(SocialActions.FellowshipRecruitOpcode,
+            BinaryPrimitives.ReadUInt32LittleEndian(body.AsSpan(8)));
+    }
+
+    [Fact]
+    public void BuildFellowshipUpdate_HasOpenBool()
+    {
+        byte[] body = SocialActions.BuildFellowshipUpdate(seq: 1, open: true);
+        Assert.Equal(SocialActions.FellowshipUpdateOpcode,
+            BinaryPrimitives.ReadUInt32LittleEndian(body.AsSpan(8)));
+        Assert.Equal(1, body[12]);
+    }
+
+    [Fact]
+    public void BuildSetCharacterOptions_HasBitmap()
+    {
+        byte[] body = SocialActions.BuildSetCharacterOptions(seq: 1, optionsBitmap: 0xDEADBEEFu);
+        Assert.Equal(0xDEADBEEFu,
+            BinaryPrimitives.ReadUInt32LittleEndian(body.AsSpan(12)));
+    }
+
+    [Fact]
+    public void BuildAddChannel_ContainsName()
+    {
+        byte[] body = SocialActions.BuildAddChannel(seq: 1, channelName: "Trade");
+        Assert.Equal(SocialActions.AddChannelOpcode,
+            BinaryPrimitives.ReadUInt32LittleEndian(body.AsSpan(8)));
+        ushort len = BinaryPrimitives.ReadUInt16LittleEndian(body.AsSpan(12));
+        Assert.Equal(5, len);
+        Assert.Equal("Trade", Encoding.ASCII.GetString(body.AsSpan(14, 5)));
+    }
+
+    [Fact]
+    public void BuildRemoveChannel_HasOpcode0x0146()
+    {
+        byte[] body = SocialActions.BuildRemoveChannel(seq: 1, channelName: "General");
+        Assert.Equal(SocialActions.RemoveChannelOpcode,
+            BinaryPrimitives.ReadUInt32LittleEndian(body.AsSpan(8)));
+    }
+}