Fetch and display day-ahead electricity spot prices from Energi Data Service

Adds a prices controller that fetches DK1/DK2 hourly spot prices via the
Energi Data Service API, stores them in PostgreSQL, and displays today's
and tomorrow's DK1 prices on the home page in øre/kWh. An HTMX "Refresh
Prices" button triggers the fetch-and-display cycle.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

resources/migrations/20260214120000-create-day-ahead-prices.up.sql

@@ -0,0 +1,8 @@
+CREATE TABLE day_ahead_prices (
+  time_utc       TIMESTAMPTZ NOT NULL,
+  time_dk        TIMESTAMP   NOT NULL,
+  price_area     VARCHAR(3)  NOT NULL,
+  price_dkk      NUMERIC(10,2),
+  price_eur      NUMERIC(10,6),
+  PRIMARY KEY (time_utc, price_area)
+);