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>

app/models.py

@@ -59,7 +59,7 @@ class Quote(Base):
 class QuoteDaily(Base):
     """Daily rollup — sparkline source. PK on (symbol, date)."""
     __tablename__ = "quotes_daily"
-    symbol: Mapped[str] = mapped_column(String(64), primary_key=True)
+    symbol: Mapped[str] = mapped_column(String(128), primary_key=True)
     date: Mapped[date] = mapped_column(Date, primary_key=True)
     close: Mapped[float | None] = mapped_column(Float)
     high: Mapped[float | None] = mapped_column(Float)
@@ -228,6 +228,7 @@ class User(Base):
     # app/services/i18n.py before writing.
     lang: Mapped[str] = mapped_column(
         String(8), nullable=False, default="en", server_default="en",
+        index=True,
     )
     # Polar (MoR) linkage — populated by the polar_webhook handler the
     # first time we see a subscription/order event for the user. The