Persist Frankfurter EUR/DKK rates in currencies table

Store daily exchange rates in PostgreSQL with EUR/DKK cross rate.
Seed rates atom from DB on startup so WebSocket works immediately
even if Frankfurter is unreachable.

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

resources/migrations/20260306200000-create-currencies.down.sql

@@ -0,0 +1 @@
+DROP TABLE currencies;

resources/migrations/20260306200000-create-currencies.up.sql

@@ -0,0 +1,7 @@
+CREATE TABLE currencies (
+  rate_date DATE PRIMARY KEY,
+  eur NUMERIC(12,6) NOT NULL,
+  dkk NUMERIC(12,6) NOT NULL,
+  eur_dkk NUMERIC(12,6) NOT NULL,
+  updated_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);

resources/queries.sql

@@ -50,3 +50,14 @@ INSERT INTO strike_price (rates, quote_sats) VALUES (:rates, :quote-sats)
 -- :name get-latest-strike-price :? :1
 -- :doc Get the most recent Strike ticker snapshot
 SELECT rates, recorded_at FROM strike_price ORDER BY id DESC LIMIT 1
+
+-- :name upsert-currency-rates! :! :n
+-- :doc Upsert daily currency rates from Frankfurter
+INSERT INTO currencies (rate_date, eur, dkk, eur_dkk, updated_at)
+VALUES (:rate-date, :eur, :dkk, :eur-dkk, NOW())
+ON CONFLICT (rate_date) DO UPDATE
+SET eur = EXCLUDED.eur, dkk = EXCLUDED.dkk, eur_dkk = EXCLUDED.eur_dkk, updated_at = NOW()
+
+-- :name get-latest-currency-rates :? :1
+-- :doc Get the most recent currency rates
+SELECT eur, dkk, eur_dkk, updated_at FROM currencies ORDER BY rate_date DESC LIMIT 1

resources/system.edn

@@ -61,7 +61,8 @@
  {:query-fn #ig/ref :db.sql/query-fn}
 
  :frankfurter/rates
- {:url #or [#env FRANKFURTER_URL "http://localhost:8080"]}
+ {:url      #or [#env FRANKFURTER_URL "http://localhost:8080"]
+  :query-fn #ig/ref :db.sql/query-fn}
 
  :strike/ticker
  {:query-fn        #ig/ref :db.sql/query-fn