add earnings-date guard — warn when a report falls in the target horizon

Finnhub's earnings calendar now supplies next_earnings_date through the
fundamentals chain; persisted on fundamental_data (migration 006) and exposed in
the fundamentals API. The recommendation panel warns when earnings fall within
the ~30-day target horizon (a report can gap price through stop/target) and
otherwise shows the next date. Informational only.

Deploy: run alembic upgrade (new fundamental_data.next_earnings_date column).

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

app/models/fundamental.py

@@ -1,6 +1,6 @@
-from datetime import datetime
+from datetime import date, datetime
 
-from sqlalchemy import DateTime, Float, ForeignKey, Text
+from sqlalchemy import Date, DateTime, Float, ForeignKey, Text
 from sqlalchemy.orm import Mapped, mapped_column, relationship
 
 from app.database import Base
@@ -17,6 +17,7 @@ class FundamentalData(Base):
     revenue_growth: Mapped[float | None] = mapped_column(Float, nullable=True)
     earnings_surprise: Mapped[float | None] = mapped_column(Float, nullable=True)
     market_cap: Mapped[float | None] = mapped_column(Float, nullable=True)
+    next_earnings_date: Mapped[date | None] = mapped_column(Date, nullable=True)
     fetched_at: Mapped[datetime] = mapped_column(
         DateTime(timezone=True), nullable=False
     )