feat(15-02): add Categories, Tags, and journal settings admin

Register the remaining YAML admin screens and the settings singleton
so a host can boot Posts, Categories, Tags, and Code journal. Posts
update and delete refuse other authors without access_other_posts.

Co-authored-by: Cursor <cursoragent@cursor.com>

controllers/posts.go

@@ -174,9 +174,28 @@ func (c postsAdminController) FormBeforeUpdate(ctx context.Context, model any) e
 	if !ok || post == nil {
 		return errors.New("posts admin: form model is not a post")
 	}
+	if err := refuseOtherAuthor(ctx, post); err != nil {
+		return err
+	}
 	return preparePostWrite(ctx, post)
 }
 
+func (c postsAdminController) FormBeforeDelete(ctx context.Context, model any) error {
+	post, ok := model.(*models.Post)
+	if !ok || post == nil {
+		return errors.New("posts admin: form model is not a post")
+	}
+	return refuseOtherAuthor(ctx, post)
+}
+
+func refuseOtherAuthor(ctx context.Context, post *models.Post) error {
+	principal, _ := bouncer.User(ctx)
+	if post.CanEdit(principal) {
+		return nil
+	}
+	return &cabana.ForbiddenError{Message: "golem15.journal::lang.journal.access_other_posts"}
+}
+
 func preparePostWrite(ctx context.Context, post *models.Post) error {
 	if err := refuseUnpublishedWrite(ctx, post); err != nil {
 		return err