feat(tags): merge repoints allowlist, embedding, aliases, fandom children

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/app/services/tag_service.py

@@ -368,18 +368,46 @@ class TagService:
         )
 
     async def _repoint_allowlist(self, src: int, tgt: int) -> None:
-        pass
+        tgt_has = await self.session.scalar(
+            select(exists().where(TagAllowlist.tag_id == tgt))
+        )
+        if tgt_has:
+            await self.session.execute(
+                text("DELETE FROM tag_allowlist WHERE tag_id = :src"),
+                {"src": src},
+            )
+        else:
+            await self.session.execute(
+                update(TagAllowlist)
+                .where(TagAllowlist.tag_id == src)
+                .values(tag_id=tgt)
+            )
 
     async def _repoint_embedding(self, src: int) -> None:
-        pass
+        await self.session.execute(
+            text(
+                "DELETE FROM tag_reference_embedding WHERE tag_id = :src"
+            ),
+            {"src": src},
+        )
 
     async def _repoint_aliases(self, src: int, tgt: int) -> None:
-        pass
+        from ..models.tag_alias import TagAlias
+
+        await self.session.execute(
+            update(TagAlias)
+            .where(TagAlias.canonical_tag_id == src)
+            .values(canonical_tag_id=tgt)
+        )
 
     async def _repoint_fandom_children(
         self, src: int, tgt: int, src_kind: TagKind
     ) -> None:
-        pass
+        if src_kind != TagKind.fandom:
+            return
+        await self.session.execute(
+            update(Tag).where(Tag.fandom_id == src).values(fandom_id=tgt)
+        )
 
     async def _create_protective_aliases(
         self, src_name: str, src_kind: TagKind, tgt: int