feat(tags): merge repoints image_tag and tag_suggestion_rejection with dedup

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

backend/app/services/tag_service.py

@@ -327,10 +327,45 @@ class TagService:
         )
 
     async def _repoint_image_tags(self, src: int, tgt: int) -> int:
-        return 0
+        """Drop source links whose image already links target, then move
+        the rest. Returns the number actually moved."""
+        await self.session.execute(
+            image_tag.delete().where(
+                and_(
+                    image_tag.c.tag_id == src,
+                    image_tag.c.image_record_id.in_(
+                        select(image_tag.c.image_record_id).where(
+                            image_tag.c.tag_id == tgt
+                        )
+                    ),
+                )
+            )
+        )
+        res = await self.session.execute(
+            image_tag.update()
+            .where(image_tag.c.tag_id == src)
+            .values(tag_id=tgt)
+        )
+        return res.rowcount or 0
 
     async def _repoint_rejections(self, src: int, tgt: int) -> None:
-        pass
+        from ..models.tag_suggestion_rejection import TagSuggestionRejection
+
+        await self.session.execute(
+            text(
+                "DELETE FROM tag_suggestion_rejection r "
+                "WHERE r.tag_id = :src AND EXISTS ("
+                "  SELECT 1 FROM tag_suggestion_rejection r2 "
+                "  WHERE r2.tag_id = :tgt "
+                "  AND r2.image_record_id = r.image_record_id)"
+            ),
+            {"src": src, "tgt": tgt},
+        )
+        await self.session.execute(
+            update(TagSuggestionRejection)
+            .where(TagSuggestionRejection.tag_id == src)
+            .values(tag_id=tgt)
+        )
 
     async def _repoint_allowlist(self, src: int, tgt: int) -> None:
         pass