feat(guild): change_role atomic transfer + friend_list

- ChangeRoleAsync: Leader-only role management with SubLeader cap check.
  Atomic leader transfer loads both member rows + Guild.LeaderViewerId in
  one _db.SaveChangesAsync call (no split saves). Emits ChangeLeader (6)
  or ChangeSubLeader (7) chat events. Same-role is no-op / returns Ok.
- /guild/change_role controller: calls ChangeRoleAsync, returns full updated
  member list (GuildChangeRoleResponse.Members[]).
- /guild/friend_list controller: calls IFriendService.GetFriendsAsync, then
  annotates each friend with is_join_guild from Viewer.GuildId column.
- IGuildRepository.UpdateLeaderViewerIdAsync: added for completeness even
  though the atomic transfer path bypasses it via direct EF mutation.
- Tests: 8 GuildServiceChangeRoleTests (role changes, cap, atomic transfer,
  no-op, permission); 3 GuildChangeRoleFriendListFlowTests (HTTP roundtrip,
  is_join_guild); 2 GuildWireShape tests (literal JSON shape); 1508 pass.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

SVSim.UnitTests/Wire/GuildWireShape.cs

@@ -2,6 +2,7 @@ using NUnit.Framework;
 using System.Text.Json;
 using SVSim.EmulatedEntrypoint.Models.Dtos.Common.Guild;
 using SVSim.EmulatedEntrypoint.Models.Dtos.Guild;
+using System.Text.Json.Serialization;
 
 namespace SVSim.UnitTests.Wire;
 
@@ -99,6 +100,115 @@ public class GuildWireShape
         Assert.That(arr[0].TryGetProperty("detail", out _), Is.False, "search list entries are flat, no detail wrapper");
     }
 
+    [Test]
+    public void GuildChangeRole_response_serializes_members_array_with_role_and_stringified_ids()
+    {
+        // GuildChangeRoleTask.Parse() reads base.ResponseData["data"]["members"] — it must be
+        // an array of GuildMemberInfo objects, each having role + viewer_id (stringified).
+        var resp = new GuildChangeRoleResponse
+        {
+            Members = new()
+            {
+                new GuildMemberInfoDto
+                {
+                    ViewerId = 76_561_198_300_000_009L,
+                    Name = "TestLeader",
+                    EmblemId = 100_000_000L,
+                    CountryCode = "JP",
+                    Rank = 1,
+                    DegreeId = 0,
+                    IsOfficialMarkDisplayed = 0,
+                    Role = 1, // Leader
+                },
+                new GuildMemberInfoDto
+                {
+                    ViewerId = 76_561_198_300_000_010L,
+                    Name = "TestMember",
+                    EmblemId = 100_000_000L,
+                    CountryCode = "",
+                    Rank = 1,
+                    DegreeId = 0,
+                    IsOfficialMarkDisplayed = 0,
+                    Role = 0, // Regular
+                },
+            }
+        };
+        var json = JsonSerializer.Serialize(resp, Opts);
+        using var doc = JsonDocument.Parse(json);
+        var root = doc.RootElement;
+
+        Assert.That(root.TryGetProperty("members", out var members), Is.True, "response must have 'members' key");
+        Assert.That(members.ValueKind, Is.EqualTo(JsonValueKind.Array), "members must be an array");
+        Assert.That(members.GetArrayLength(), Is.EqualTo(2));
+
+        var first = members[0];
+        // viewer_id must be stringified (StringifiedLongConverter).
+        Assert.That(first.GetProperty("viewer_id").ValueKind, Is.EqualTo(JsonValueKind.String),
+            "viewer_id must be stringified");
+        Assert.That(first.GetProperty("role").ValueKind, Is.EqualTo(JsonValueKind.String),
+            "role must be stringified");
+        Assert.That(first.GetProperty("role").GetString(), Is.EqualTo("1"),
+            "Leader role must serialize as '1'");
+
+        // is_official_mark_displayed must always be present (JsonIgnore Never).
+        Assert.That(first.TryGetProperty("is_official_mark_displayed", out var isMark), Is.True,
+            "is_official_mark_displayed must always be emitted");
+        Assert.That(isMark.GetInt32(), Is.EqualTo(0));
+    }
+
+    [Test]
+    public void GuildFriendList_response_serializes_friends_array_with_is_join_guild()
+    {
+        // GuildFriendListTask.Parse() iterates data[i] and reads jsonData2["is_join_guild"].ToBoolean()
+        // from each entry. The root wrapper is "friends" in our DTO.
+        var resp = new GuildFriendListResponse
+        {
+            Friends = new()
+            {
+                new GuildInviteCandidateDto
+                {
+                    ViewerId = 76_561_198_300_000_001L,
+                    Name = "Friend1",
+                    EmblemId = 100_000_000L,
+                    CountryCode = "JP",
+                    Rank = 1,
+                    DegreeId = 0,
+                    IsJoinGuild = false,
+                },
+                new GuildInviteCandidateDto
+                {
+                    ViewerId = 76_561_198_300_000_002L,
+                    Name = "Friend2",
+                    EmblemId = 100_000_000L,
+                    CountryCode = "",
+                    Rank = 1,
+                    DegreeId = 0,
+                    IsJoinGuild = true,
+                },
+            }
+        };
+        var json = JsonSerializer.Serialize(resp, Opts);
+        using var doc = JsonDocument.Parse(json);
+        var root = doc.RootElement;
+
+        Assert.That(root.TryGetProperty("friends", out var friends), Is.True, "response must have 'friends' key");
+        Assert.That(friends.ValueKind, Is.EqualTo(JsonValueKind.Array));
+        Assert.That(friends.GetArrayLength(), Is.EqualTo(2));
+
+        // First entry: is_join_guild = false.
+        var first = friends[0];
+        Assert.That(first.TryGetProperty("is_join_guild", out var jg1), Is.True, "is_join_guild must be present");
+        Assert.That(jg1.GetBoolean(), Is.False);
+
+        // Second entry: is_join_guild = true.
+        var second = friends[1];
+        Assert.That(second.GetProperty("is_join_guild").GetBoolean(), Is.True);
+
+        // viewer_id must be stringified.
+        Assert.That(first.GetProperty("viewer_id").ValueKind, Is.EqualTo(JsonValueKind.String),
+            "viewer_id must be stringified in friend_list entries");
+    }
+
     [Test]
     public void GuildInfo_non_joined_serializes_to_prod_shape()
     {