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>

deps.edn

@@ -25,7 +25,8 @@
  io.github.kit-clj/kit-postgres {:mvn/version "1.0.7"}
  io.github.kit-clj/kit-sql-conman {:mvn/version "1.10.5"}
  io.github.kit-clj/kit-sql-migratus {:mvn/version "1.0.5"}
- hiccup/hiccup {:mvn/version "2.0.0"}}
+ hiccup/hiccup {:mvn/version "2.0.0"}
+ org.clojure/data.json {:mvn/version "2.5.1"}}
  :aliases {:build {:deps {io.github.clojure/tools.build {:mvn/version "0.10.11"}}
                    :ns-default build}