Dividend yield + forward calendar for a ticker

GET /api/dividend-forecast response. F4 schema-tightening + correction (2026-04-30): forecast and annualTotal REQUIRED. Handler returns {"forecast": [...], "annualTotal": N} on every 200 path (empty-tickers, success, exception fallback); 400/500 branches use ErrorResponse.

Frontend calendar-view.js:367-368 reads data.forecast and data.annualTotal to drive the dividend-income projection card.

Note: previously declared per-ticker fields (ticker, currentYield, annualDividend, nextExDate, payoutHistory) at the top level — NONE of which the handler returns. The handler's actual wire format is a list-wrapper. Schema rewritten to match reality.