fix(guild): emit is_friend / is_friend_apply in /guild/info members

GuildMemberInfo.cs:48-49 re-reads json["is_friend"] / json["is_friend_apply"]
UNGUARDED on top of the base-class UserInfoBase's guarded read. Our DTO had
them as int? with global WhenWritingNull → keys omitted → LitJson threw
KeyNotFoundException, crashing the client right after guild create.

Flip the fields to non-nullable int with JsonIgnoreCondition.Never so they
always ship, and wire a batched IFriendService.GetFriendRelationsAsync
lookup so the values are actually populated (single Contains-batched query
per relation table).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

SVSim.Database/Services/Friend/FriendDtos.cs

@@ -82,3 +82,9 @@ public sealed record BattleParticipationContext(
     int BattleType,
     int DeckFormat,
     int TwoPickType);
+
+/// <summary>
+/// Caller-relative friend flags for another viewer. Used to badge rows in guild-member,
+/// invite-candidate, and join-request lists on the wire (<c>is_friend</c>, <c>is_friend_apply</c>).
+/// </summary>
+public sealed record FriendRelation(bool IsFriend, bool HasOutgoingApply);

SVSim.Database/Services/Friend/FriendService.cs

@@ -313,6 +313,36 @@ public sealed class FriendService : IFriendService, IPlayedTogetherWriter
         await _db.SaveChangesAsync(ct);
     }
 
+    public async Task<IReadOnlyDictionary<long, FriendRelation>> GetFriendRelationsAsync(
+        long viewerId, IReadOnlyList<long> otherViewerIds, CancellationToken ct)
+    {
+        if (otherViewerIds.Count == 0)
+            return new Dictionary<long, FriendRelation>();
+
+        var idSet = otherViewerIds.Where(id => id != viewerId).Distinct().ToList();
+        var friendSet = idSet.Count == 0
+            ? new HashSet<long>()
+            : (await _db.ViewerFriends.AsNoTracking()
+                .Where(f => f.OwnerViewerId == viewerId && idSet.Contains(f.FriendViewerId))
+                .Select(f => f.FriendViewerId)
+                .ToListAsync(ct)).ToHashSet();
+        var applySet = idSet.Count == 0
+            ? new HashSet<long>()
+            : (await _db.ViewerFriendApplies.AsNoTracking()
+                .Where(a => a.FromViewerId == viewerId && idSet.Contains(a.ToViewerId))
+                .Select(a => a.ToViewerId)
+                .ToListAsync(ct)).ToHashSet();
+
+        var result = new Dictionary<long, FriendRelation>(otherViewerIds.Count);
+        foreach (var id in otherViewerIds)
+        {
+            result[id] = id == viewerId
+                ? new FriendRelation(false, false)
+                : new FriendRelation(friendSet.Contains(id), applySet.Contains(id));
+        }
+        return result;
+    }
+
     // --- helpers ---
 
     private sealed record ViewerProjection(

SVSim.Database/Services/Friend/IFriendService.cs

@@ -27,4 +27,12 @@ public interface IFriendService
 
     /// <summary>Deletes both directions of the friendship (A→B and B→A).</summary>
     Task RejectFriendAsync(long viewerId, int targetViewerId, CancellationToken ct);
+
+    /// <summary>
+    /// Batched caller-relative friend-relation lookup. For each id in <paramref name="otherViewerIds"/>
+    /// returns whether the caller is already friends with them and/or has an outgoing pending apply
+    /// to them. Self and unknown ids resolve to <c>(false, false)</c>.
+    /// </summary>
+    Task<IReadOnlyDictionary<long, FriendRelation>> GetFriendRelationsAsync(
+        long viewerId, IReadOnlyList<long> otherViewerIds, CancellationToken ct);
 }