ci: repair autogenerate's missing pgvector import before applying (#3275)

mode: models applies the raw autogenerated candidate, and it cannot run:

  sa.Column('weights', pgvector.sqlalchemy.vector.VECTOR(dim=1152), ...)
  NameError: name 'pgvector' is not defined

Alembic emits the qualified reference without emitting the import.
Observed on run 4988, which turns this from a thing I predicted by
reading the candidate into a thing demonstrated by executing it.

Repaired in the workflow rather than counted as a schema difference: the
comparison asks whether the MODELS describe the schema, and this is a
defect in the generator. The same fixup has to be applied by hand to any
baseline generated this way, which is why it is item 4 on the collapsed
baseline's hand-written list.

.forgejo/workflows/baseline.yml

@@ -208,6 +208,15 @@ jobs:
             mkdir -p /tmp/held
             mv alembic/versions/*.py /tmp/held/
             cp /tmp/candidate/*.py alembic/versions/
+            # Autogenerate EMITS pgvector.sqlalchemy.vector.VECTOR(...) without
+            # importing it, so the file it writes cannot run:
+            #   NameError: name 'pgvector' is not defined
+            # Observed on run 4988, which is the proof rather than the theory.
+            # This is a defect in the GENERATOR, not in the models, so it is
+            # repaired here rather than counted as a schema difference — the
+            # comparison is about whether the models describe the schema.
+            sed -i '0,/^import sqlalchemy as sa$/s//import sqlalchemy as sa\nimport pgvector.sqlalchemy.vector/' alembic/versions/*.py
+            grep -n 'import pgvector' alembic/versions/*.py
             ls alembic/versions/*.py
             DB_NAME=fc_base alembic upgrade head
             rm -f alembic/versions/*.py