feat(fp): WP-23 — org-template backend + admin role

Second template axis (org identity: letterhead, footer, signature,
margins) server-side: OrgTemplateStore with JSON version history,
publish/rollback, sent-brief version pinning, admin role + capability,
5 admin endpoints, org-logo upload category. FE seam widened only
(Role/Capability unions, interceptor); WP-24/26 consume it.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

backend/src/BigRegister.Api/Data/Migrations/AppDbContextModelSnapshot.cs

@@ -124,10 +124,17 @@ namespace BigRegister.Api.Data.Migrations
                         .IsRequired()
                         .HasColumnType("TEXT");
 
+                    b.Property<int?>("SentOrgTemplateVersion")
+                        .HasColumnType("INTEGER");
+
                     b.Property<string>("Status")
                         .IsRequired()
                         .HasColumnType("TEXT");
 
+                    b.Property<string>("SubOrgId")
+                        .IsRequired()
+                        .HasColumnType("TEXT");
+
                     b.Property<string>("TemplateId")
                         .IsRequired()
                         .HasColumnType("TEXT");
@@ -140,6 +147,27 @@ namespace BigRegister.Api.Data.Migrations
                     b.ToTable("Briefs");
                 });
 
+            modelBuilder.Entity("BigRegister.Api.Data.OrgTemplateEntity", b =>
+                {
+                    b.Property<string>("SubOrgId")
+                        .HasColumnType("TEXT");
+
+                    b.Property<string>("Draft")
+                        .IsRequired()
+                        .HasColumnType("TEXT");
+
+                    b.Property<string>("History")
+                        .IsRequired()
+                        .HasColumnType("TEXT");
+
+                    b.Property<int>("PublishedVersion")
+                        .HasColumnType("INTEGER");
+
+                    b.HasKey("SubOrgId");
+
+                    b.ToTable("OrgTemplates");
+                });
+
             modelBuilder.Entity("BigRegister.Api.Data.StoredDocument", b =>
                 {
                     b.Property<string>("DocumentId")