New `elprice` table with a simpler shape (time_dk, price_area,
price_dkk) backing a JSON endpoint that returns hourly DK1 + DK2
prices for any date. Cache-miss path fetches from the same
DayAheadPrices dataset as day_ahead_prices, upserts, and returns.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>