fix(guild): final-review remediation — replay_detail flat, FK on leader, transaction wraps, _db extraction

C1: replay_detail — flatten stored payload to data level. ChatReplayDetailTask.Parse() calls
new ReplayDetailInfo(data) which unguardedly accesses data[battleId], data[seed], data[vid1],
etc. Wrapping under replay_info key crashes the client. Controller now returns Ok(JsonElement)
directly so stored battle fields are at data root. Wire-shape test added.

C2: Guild.LeaderViewerId long to long?; add HasOne<Viewer> FK with OnDelete=SetNull; migration
AddGuildLeaderViewerIdFk; all consumers null-guarded with ?? 0L.

C3: BreakupAsync — wrap 6 destructive ops in IDbContextTransaction with InMemory fallback.

C4: CommitJoinAsync — wrap member-add + viewer-guildId-set + invite/request cleanup in
IDbContextTransaction with InMemory fallback. Chat event emitted after commit.

I1: GuildController — remove SVSimDbContext field; inject IViewerRepository + IGuildMemberRepository.
Add IGuildMemberRepository.GetViewerIdsInAGuildAsync (batch guild-membership check).
All _db.Viewers / _db.GuildMembers queries replaced with repo calls.

I2: GuildService — extract 3 _db.Viewers queries: GetEquippedEmblemIdAsync (CreateAsync),
LoadGuildProfileBatchAsync (ListOutgoingInvitesAsync + ListPendingJoinRequestsForMyGuildAsync).
Add GuildMemberProfile record with IsOfficialMarkDisplayed. GetEmblemListAsync for EmblemList.

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

SVSim.Database/Migrations/SVSimDbContextModelSnapshot.cs

@@ -110,7 +110,7 @@ namespace SVSim.Database.Migrations
                     b.Property<int>("JoinCondition")
                         .HasColumnType("integer");
 
-                    b.Property<long>("LeaderViewerId")
+                    b.Property<long?>("LeaderViewerId")
                         .HasColumnType("bigint");
 
                     b.Property<string>("Name")
@@ -120,6 +120,8 @@ namespace SVSim.Database.Migrations
 
                     b.HasKey("GuildId");
 
+                    b.HasIndex("LeaderViewerId");
+
                     b.HasIndex("Name");
 
                     b.ToTable("Guilds");
@@ -3653,6 +3655,14 @@ namespace SVSim.Database.Migrations
                         .IsRequired();
                 });
 
+            modelBuilder.Entity("SVSim.Database.Entities.Guild.Guild", b =>
+                {
+                    b.HasOne("SVSim.Database.Models.Viewer", null)
+                        .WithMany()
+                        .HasForeignKey("LeaderViewerId")
+                        .OnDelete(DeleteBehavior.SetNull);
+                });
+
             modelBuilder.Entity("SVSim.Database.Entities.Guild.GuildChatMessage", b =>
                 {
                     b.HasOne("SVSim.Database.Entities.Guild.Guild", "Guild")