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>

tests/unit/test_fundamentals_chain_provider.py

@@ -153,3 +153,29 @@ async def test_rate_limited_but_complete_does_not_raise():
 
     result = await provider.fetch_fundamentals("AAPL")
     assert result.pe_ratio == 20.0
+
+
+@pytest.mark.asyncio
+async def test_chain_merges_next_earnings_date():
+    """Earnings date is taken from the first provider that supplies it."""
+    from datetime import date as _date
+
+    primary = FundamentalData(
+        ticker="AAPL", pe_ratio=None, revenue_growth=None, earnings_surprise=None,
+        market_cap=100.0, fetched_at=datetime.now(timezone.utc),
+    )
+
+    class _EarningsProvider:
+        async def fetch_fundamentals(self, ticker: str) -> FundamentalData:
+            return FundamentalData(
+                ticker=ticker, pe_ratio=10.0, revenue_growth=5.0, earnings_surprise=1.0,
+                market_cap=None, fetched_at=datetime.now(timezone.utc),
+                next_earnings_date=_date(2026, 7, 1),
+            )
+
+    provider = ChainedFundamentalProvider([
+        ("fmp", _DataProvider(primary)),
+        ("finnhub", _EarningsProvider()),
+    ])
+    result = await provider.fetch_fundamentals("AAPL")
+    assert result.next_earnings_date == _date(2026, 7, 1)