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/system.edn

@@ -66,4 +66,5 @@
   :db {:datasource #ig/ref :db.sql/connection}
   :migrate-on-init? true}
  :reitit.routes/ui {:base-path "",
-                    :env #ig/ref :system/env}}
+                    :env #ig/ref :system/env
+                    :query-fn #ig/ref :db.sql/query-fn}}