fix(alembic): renumber benchmark migration 011 -> 012

011 collided with the existing 011_add_regime_snapshots (duplicate revision id
and a second head branching off 010), which broke `alembic upgrade head`. Chain
the benchmark_prices migration after regime_snapshots so the history is linear
again (010 -> 011 regime_snapshots -> 012 benchmark_prices, single head).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

alembic/versions/012_add_benchmark_prices.py

@@ -0,0 +1,41 @@
+"""add benchmark_prices
+
+Stores daily closes for a benchmark index (SPY) so paper-trade alpha — trade
+return minus the benchmark's return over the same holding period — can be
+computed. Kept separate from the tradeable universe: the benchmark is not a
+Ticker, so it never enters the scanner, momentum ranking, or rankings.
+
+Revision ID: 012
+Revises: 011
+Create Date: 2026-06-28 00:00:00.000000
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision: str = "012"
+down_revision: Union[str, None] = "011"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        "benchmark_prices",
+        sa.Column("id", sa.Integer(), nullable=False),
+        sa.Column("symbol", sa.String(length=20), nullable=False),
+        sa.Column("date", sa.Date(), nullable=False),
+        sa.Column("close", sa.Float(), nullable=False),
+        sa.PrimaryKeyConstraint("id"),
+        sa.UniqueConstraint("symbol", "date", name="uq_benchmark_symbol_date"),
+    )
+    op.create_index("ix_benchmark_prices_symbol", "benchmark_prices", ["symbol"])
+
+
+def downgrade() -> None:
+    op.drop_index("ix_benchmark_prices_symbol", table_name="benchmark_prices")
+    op.drop_table("benchmark_prices")