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.EmulatedEntrypoint/Controllers/GuildController.cs

@@ -5,6 +5,7 @@ using SVSim.Database.Entities.Guild;
 using SVSim.Database.Models;
 using SVSim.Database.Models.Config;
 using SVSim.Database.Services;
+using SVSim.Database.Services.Friend;
 using SVSim.Database.Services.Guild;
 using SVSim.EmulatedEntrypoint.Models.Dtos.Common;
 using SVSim.EmulatedEntrypoint.Models.Dtos.Common.Guild;
@@ -20,15 +21,17 @@ public sealed class GuildController : SVSimController
     private readonly IGuildService _guild;
     private readonly IGameConfigService _configs;
     private readonly SVSimDbContext _db;
+    private readonly IFriendService _friends;
 
     // Wire error code returned when guild operations fail (non-1 result_code).
     private const int GuildErrorResultCode = 2;
 
-    public GuildController(IGuildService guild, IGameConfigService configs, SVSimDbContext db)
+    public GuildController(IGuildService guild, IGameConfigService configs, SVSimDbContext db, IFriendService friends)
     {
         _guild = guild;
         _configs = configs;
         _db = db;
+        _friends = friends;
     }
 
     [HttpPost("info")]
@@ -171,8 +174,40 @@ public sealed class GuildController : SVSimController
     }
 
     [HttpPost("friend_list")]
-    public Task<ActionResult<GuildFriendListResponse>> FriendList([FromBody] BaseRequest _, CancellationToken ct)
-        => Task.FromResult<ActionResult<GuildFriendListResponse>>(new GuildFriendListResponse { Friends = new() });
+    public async Task<ActionResult<GuildFriendListResponse>> FriendList([FromBody] BaseRequest _, CancellationToken ct)
+    {
+        if (!TryGetViewerId(out var viewerId)) return Unauthorized();
+
+        var friendInfo = await _friends.GetFriendsAsync(viewerId, ct);
+        if (friendInfo.Friends.Count == 0)
+            return new GuildFriendListResponse { Friends = new() };
+
+        // For each friend, determine if they are already in a guild (is_join_guild).
+        var friendViewerIds = friendInfo.Friends.Select(f => (long)f.ViewerId).ToList();
+        var viewerRows = await _db.Viewers
+            .AsNoTracking()
+            .Where(v => friendViewerIds.Contains(v.Id))
+            .Select(v => new { v.Id, v.GuildId })
+            .ToDictionaryAsync(v => v.Id, v => v.GuildId, ct);
+
+        var candidates = new List<GuildInviteCandidateDto>(friendInfo.Friends.Count);
+        foreach (var f in friendInfo.Friends)
+        {
+            viewerRows.TryGetValue(f.ViewerId, out var guildId);
+            candidates.Add(new GuildInviteCandidateDto
+            {
+                ViewerId    = f.ViewerId,
+                Name        = f.Name,
+                EmblemId    = f.EmblemId,
+                CountryCode = f.CountryCode,
+                Rank        = f.Rank,
+                DegreeId    = f.DegreeId,
+                IsJoinGuild = guildId is not null,
+            });
+        }
+
+        return new GuildFriendListResponse { Friends = candidates };
+    }
 
     [HttpPost("invite_user_list")]
     public async Task<ActionResult<GuildInviteUserListResponse>> InviteUserList([FromBody] BaseRequest _, CancellationToken ct)
@@ -315,8 +350,23 @@ public sealed class GuildController : SVSimController
     }
 
     [HttpPost("change_role")]
-    public Task<ActionResult<GuildChangeRoleResponse>> ChangeRole([FromBody] GuildChangeRoleRequest req, CancellationToken ct)
-        => Task.FromResult<ActionResult<GuildChangeRoleResponse>>(new GuildChangeRoleResponse { Members = new() });
+    public async Task<ActionResult<GuildChangeRoleResponse>> ChangeRole([FromBody] GuildChangeRoleRequest req, CancellationToken ct)
+    {
+        if (!TryGetViewerId(out var viewerId)) return Unauthorized();
+        var r = await _guild.ChangeRoleAsync(viewerId, req.TargetViewerId, req.RoleId, ct);
+        if (!r.IsOk) return WireError();
+
+        // Load caller's membership to get the guild id, then return the full updated member list.
+        var membership = await _db.GuildMembers.FirstOrDefaultAsync(m => m.ViewerId == viewerId, ct);
+        if (membership is null) return WireError();
+
+        var members = await _db.GuildMembers
+            .Where(m => m.GuildId == membership.GuildId)
+            .ToListAsync(ct);
+
+        var memberDtos = await ToMemberDtoListAsync(members, viewerId, ct);
+        return new GuildChangeRoleResponse { Members = memberDtos };
+    }
 
     // ===== Private helpers =====