remove dead 'Comment' field from CircleAuthorizationToBlogPost

The bool Comment on CircleAuthorizationToBlogPost was dead code:
never read or written by any caller in src/, no UI exposure, no
behavioural semantics. The wire DTO (CircleAuthorization in
Yavsc.Abstract) doesn't carry it, no reader consumes it, and the
PostIt client builds its payload without it.

What changes:
- src/Yavsc.Server/Models/Access/CircleAuthorizationToBlogPost.cs:
  remove the property.
- src/Yavsc.Blogs.Tests/BlogAclApiTests.cs: drop 'Comment = true'
  from the existing test payload and trim the now-inaccurate XML
  doc comment ('CircleId + BlogPostId + Comment' -> 'CircleId +
  BlogPostId'). Also adds a new [Fact] pinning the prod bug
  reported on 2026-08-21 (HTTP 500 'BlogPostId is unknown' when
  PostIt POSTs the bare { circleId } shape). That test stays red:
  the real fix for the 500 is in PostIt (payload needs blogPostId)
  + on the wire DTO + server-side validation, and lives in a
  follow-up commit.

Migration:
- src/Yavsc.Org/Migrations/20260820232152_DropCommentFromCircleAuthorizationToBlogPost
  drops the boolean 'Comment' column on CircleAuthorizationToBlogPost.
  The generated scaffold also wanted to drop three 'ClientId1'
  shadow FK columns on ClientScopes / ClientRedirectUris /
  ClientGrantTypes (from leftover HasOne<Client>() overrides in
  ApplicationDbContext.OnModelCreating); those were removed from
  the .cs to keep the migration scoped to this fix. Cleaning up the
  shadow property declarations themselves is left as a separate
  task.

The ModelSnapshot still reflects the shadow 'ClientId1' columns
intentionally: they exist in the prod database today (all NULL),
and EF will rescaffold a drop migration for them on the next
'migrations add' regardless. No data loss.

src/Yavsc.Server/Models/Access/CircleAuthorizationToBlogPost.cs

@@ -19,8 +19,5 @@ namespace Yavsc.Models.Access
         [ForeignKey("CircleId")]
         public virtual Circle Allowed { get; set; }
 
-        public bool Comment { get; set; }
-        
-
     }
 }