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/providers/protocol.py

@@ -53,6 +53,7 @@ class FundamentalData:
     earnings_surprise: float | None
     market_cap: float | None
     fetched_at: datetime
+    next_earnings_date: date | None = None
     unavailable_fields: dict[str, str] = field(default_factory=dict)