fix(risk-monitor): drop an unused import and align migration 033 with its model

ruff F401 failed the deploy: `import pytest` in test_event_study.py outlived the
pytest.approx assertion it was added for.

Compiling the migration for Postgres while checking that turned up a second
defect worth fixing while the table is still empty. It created a unique
constraint *and* a plain index on effective_date, while the model declares
`unique=True, index=True` -- one unique index. Both enforce uniqueness, but the
pairing left a redundant second index on the column and a permanent diff for
autogenerate to keep trying to reconcile. Now renders byte-for-byte what the
model declares, matching RegimeSnapshot.date.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

alembic/versions/033_regime_fundamental_observations.py

@@ -48,14 +48,17 @@ def upgrade() -> None:
         sa.Column("fetched_at", sa.DateTime(timezone=True), nullable=False),
         sa.Column("created_at", sa.DateTime(timezone=True), nullable=False),
         sa.PrimaryKeyConstraint("id"),
-        sa.UniqueConstraint(
-            "effective_date", name="uq_regime_fundamental_observations_effective_date"
-        ),
     )
+    # One unique index, not a unique constraint plus a plain index: the model
+    # declares `unique=True, index=True`, which SQLAlchemy renders as exactly
+    # this. The constraint-plus-index pairing worked but left a redundant second
+    # index on the column and a permanent metadata diff for autogenerate to keep
+    # trying to reconcile. Matches RegimeSnapshot.date, the sibling table.
     op.create_index(
         "ix_regime_fundamental_observations_effective_date",
         "regime_fundamental_observations",
         ["effective_date"],
+        unique=True,
     )
 
 

tests/unit/test_event_study.py

@@ -5,8 +5,6 @@ from __future__ import annotations
 from copy import deepcopy
 from datetime import date, timedelta
 
-import pytest
-
 from app.services.breadth_service import _breadth_from_closes, compute_divergence_series
 from app.services.event_study_service import (
     MIN_EVENTS_FOR_CONFIDENCE,