alembic: 0023 — users.lang index + widen quotes_daily.symbol

Two related schema fixes from the code review:

- users.lang gets a single-column index. The ai_log_job and
  email_digest_job both SELECT DISTINCT on this column every cycle;
  even at low cardinality an index is the right shape.
- quotes_daily.symbol widened to VARCHAR(128) to match quotes.symbol
  (widened back in 0005). Long Eurostat/ONS symbols would silently
  truncate during rollup otherwise.

Models updated to match (User.lang gains index=True, QuoteDaily.symbol
goes to String(128)).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

alembic/versions/0023_lang_index_and_qd_symbol_widen.py

@@ -0,0 +1,38 @@
+"""users.lang index + widen quotes_daily.symbol to VARCHAR(128).
+
+Revision ID: 0023
+Revises: 0022
+Create Date: 2026-05-27
+"""
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+from alembic import op
+
+
+revision: str = "0023"
+down_revision: Union[str, None] = "0022"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.create_index("ix_users_lang", "users", ["lang"])
+    op.alter_column(
+        "quotes_daily",
+        "symbol",
+        existing_type=sa.String(length=64),
+        type_=sa.String(length=128),
+        existing_nullable=False,
+    )
+
+
+def downgrade() -> None:
+    op.alter_column(
+        "quotes_daily",
+        "symbol",
+        existing_type=sa.String(length=128),
+        type_=sa.String(length=64),
+        existing_nullable=False,
+    )
+    op.drop_index("ix_users_lang", table_name="users")