capsite: public-origin candidate: sync (as in bib sync #195)

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

social-coop-checklist.md

@@ -102,6 +102,9 @@ sit under each goal.
                 becomes a post). Those need *write* authority, which
                 no cache holds today: each would be a new, narrowly
                 minted capability, not a widening of the read tokens.
+              - `sync.madmode.com`: the word
+                [bib sync #195](https://github.com/dckc/madmode-blog/issues/195)
+                already uses; two-way like `syndicate`, plainer.
               The follower actor's handle follows the hostname
               (e.g. `@dckc@peers.madmode.com`).
         - [ ] 8-iii. Neither reaches favourites, bookmarks, or