Fix AP re-publish: use versioned object IDs after Delete

After Delete + re-Create, Mastodon tombstones the old object ID and
ignores new Creates with the same ID. Now appends /v2, /v3 etc. so
remote servers treat re-publishes as fresh posts.

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

contracts/protocols.py

@@ -216,6 +216,11 @@ class FederationService(Protocol):
         self, session: AsyncSession, source_type: str, source_id: int,
     ) -> APActivityDTO | None: ...
 
+    async def count_activities_for_source(
+        self, session: AsyncSession, source_type: str, source_id: int,
+        *, activity_type: str,
+    ) -> int: ...
+
     # -- Followers ------------------------------------------------------------
     async def get_followers(
         self, session: AsyncSession, username: str,