Fix URL encoding of JSON filter parameter in API request

URI/create rejects raw braces/brackets in query strings. URL-encode the
filter JSON so the request succeeds.

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

src/clj/pmagnus/elprice/web/controllers/prices.clj

@@ -3,7 +3,7 @@
    [clojure.data.json :as json]
    [clojure.tools.logging :as log])
   (:import
-   [java.net URI]
+   [java.net URI URLEncoder]
    [java.net.http HttpClient HttpRequest HttpResponse$BodyHandlers]
    [java.time LocalDate ZoneId]
    [java.time.format DateTimeFormatter]
@@ -19,7 +19,7 @@
   (str "https://api.energidataservice.dk/dataset/DayAheadPrices"
        "?start=" start-date
        "&end=" end-date
-       "&filter=" (json/write-str {"PriceArea" ["DK1" "DK2"]})
+       "&filter=" (URLEncoder/encode (json/write-str {"PriceArea" ["DK1" "DK2"]}) "UTF-8")
        "&sort=TimeDK%20asc"
        "&limit=200"))