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>

services/federation_impl.py

@@ -288,6 +288,20 @@ class SqlFederationService:
         ).scalars().first()
         return _activity_to_dto(a) if a else None
 
+    async def count_activities_for_source(
+        self, session: AsyncSession, source_type: str, source_id: int,
+        *, activity_type: str,
+    ) -> int:
+        from sqlalchemy import func
+        result = await session.execute(
+            select(func.count()).select_from(APActivity).where(
+                APActivity.source_type == source_type,
+                APActivity.source_id == source_id,
+                APActivity.activity_type == activity_type,
+            )
+        )
+        return result.scalar_one()
+
     # -- Followers ------------------------------------------------------------
 
     async def get_followers(