fix(alembic 0025): qualify ambiguous post.id / post.source_id in fragment-group SELECT (post JOIN source — both have id)

alembic/versions/0025_fix_subscribestar_post_ids.py

@@ -188,12 +188,13 @@ def upgrade() -> None:
     # Merge to one canonical row. Pre-handle the same ImageProvenance
     # collision pattern as alembic 0022 (uq_image_provenance_image_post).
     fragment_groups = conn.execute(text("""
-        SELECT source_id, external_post_id, ARRAY_AGG(id ORDER BY id ASC) AS post_ids
+        SELECT p.source_id, p.external_post_id,
+               ARRAY_AGG(p.id ORDER BY p.id ASC) AS post_ids
         FROM post p
         JOIN source s ON s.id = p.source_id
         WHERE s.platform = 'subscribestar'
           AND p.external_post_id IS NOT NULL
-        GROUP BY source_id, external_post_id
+        GROUP BY p.source_id, p.external_post_id
         HAVING COUNT(*) > 1
     """)).fetchall()