Add tariff_dkk + total_dkk to elprice

Each hourly row now carries the N1 time-of-use tariff (øre/kWh × 10
to match the DKK/MWh unit of price_dkk) and the combined consumer
price (spot + tariff). Existing rows are backfilled in the migration
with a CASE expression mirroring tariffs/tariff-for-hour; new writes
compute it in the controller. API response exposes both fields.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

resources/migrations/20260419020000-add-elprice-tariff-total.up.sql

@@ -0,0 +1,21 @@
+ALTER TABLE elprice ADD COLUMN tariff_dkk NUMERIC(10,2);
+--;;
+ALTER TABLE elprice ADD COLUMN total_dkk NUMERIC(10,2);
+--;;
+UPDATE elprice
+   SET tariff_dkk = CASE
+     WHEN EXTRACT(MONTH FROM time_dk) BETWEEN 4 AND 9 THEN
+       CASE
+         WHEN EXTRACT(HOUR FROM time_dk) < 6                              THEN 109.80
+         WHEN EXTRACT(HOUR FROM time_dk) >= 17 AND EXTRACT(HOUR FROM time_dk) < 21 THEN 428.30
+         ELSE                                                                  164.70
+       END
+     ELSE
+       CASE
+         WHEN EXTRACT(HOUR FROM time_dk) < 6                              THEN 109.80
+         WHEN EXTRACT(HOUR FROM time_dk) >= 17 AND EXTRACT(HOUR FROM time_dk) < 21 THEN 988.40
+         ELSE                                                                  329.50
+       END
+   END;
+--;;
+UPDATE elprice SET total_dkk = price_dkk + tariff_dkk WHERE tariff_dkk IS NOT NULL;