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>

frontend/src/lib/types.ts

@@ -285,6 +285,7 @@ export interface FundamentalResponse {
   revenue_growth: number | null;
   earnings_surprise: number | null;
   market_cap: number | null;
+  next_earnings_date: string | null;
   fetched_at: string | null;
   unavailable_fields: Record<string, string>;
 }