Renumber the lowercase-email migration to 011

The security-audit branch added it as revision 009 while main had already
taken 009 (day_assertion) and 010 (drop pinned/exclusion), leaving Alembic
with two heads and every migration test failing after the merge. It now
revises 010.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01T4wjgbVL4HAC5Rdaw75VbV

backend/migrations/versions/011_lowercase_user_email.py

@@ -19,8 +19,8 @@ re-run the migration, rather than facing a half-applied state.
 `downgrade()` cannot restore the original casing (it was never recorded) —
 it is a deliberate, documented no-op. Lowercasing is a one-way normalization.
 
-Revision ID: 009
-Revises: 008
+Revision ID: 011
+Revises: 010
 Create Date: 2026-09-20
 """
 
@@ -30,8 +30,8 @@ from typing import Any
 
 from alembic import op
 
-revision: str = "009"
-down_revision: str | None = "008"
+revision: str = "011"
+down_revision: str | None = "010"
 branch_labels: str | None = None
 depends_on: str | None = None