fix(migration): use canonical fk_<table>_<col>_<ref> names per Base naming_convention

alembic/versions/0030_nullable_post_source_id_denorm_artist_id.py

@@ -50,12 +50,14 @@ def upgrade() -> None:
     conn = op.get_bind()
 
     # Step 1: add Post.artist_id, initially nullable for backfill.
+    # FK naming follows the Base.metadata naming_convention
+    # (fk_<table>_<column>_<referred_table>) — alembic 0001 set this up.
     op.add_column(
         "post",
         sa.Column("artist_id", sa.Integer, nullable=True),
     )
     op.create_foreign_key(
-        "post_artist_id_fkey", "post", "artist",
+        "fk_post_artist_id_artist", "post", "artist",
         ["artist_id"], ["id"], ondelete="CASCADE",
     )
 
@@ -82,22 +84,24 @@ def upgrade() -> None:
     op.alter_column("post", "artist_id", nullable=False)
     op.create_index("ix_post_artist_id", "post", ["artist_id"])
 
-    # Step 4: relax post.source_id + flip FK to SET NULL.
+    # Step 4: relax post.source_id + flip FK to SET NULL. The original FK
+    # name from alembic 0001 is `fk_post_source_id_source` per the
+    # NAMING_CONVENTION in models/base.py.
     op.alter_column("post", "source_id", nullable=True)
-    op.drop_constraint("post_source_id_fkey", "post", type_="foreignkey")
+    op.drop_constraint("fk_post_source_id_source", "post", type_="foreignkey")
     op.create_foreign_key(
-        "post_source_id_fkey", "post", "source",
+        "fk_post_source_id_source", "post", "source",
         ["source_id"], ["id"], ondelete="SET NULL",
     )
 
     # Step 5: relax image_provenance.source_id + flip FK to SET NULL.
     op.alter_column("image_provenance", "source_id", nullable=True)
     op.drop_constraint(
-        "image_provenance_source_id_fkey", "image_provenance",
+        "fk_image_provenance_source_id_source", "image_provenance",
         type_="foreignkey",
     )
     op.create_foreign_key(
-        "image_provenance_source_id_fkey", "image_provenance", "source",
+        "fk_image_provenance_source_id_source", "image_provenance", "source",
         ["source_id"], ["id"], ondelete="SET NULL",
     )