Fall back to DB for price when Binance websocket not connected

The /api/price/latest endpoint now reads the latest row from
binance_price table when the in-memory atom is empty on startup.

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

src/clj/pmagnus/btcdata/web/routes/api.clj

@@ -87,10 +87,14 @@
      {:on-open (fn [{:keys [^WebSocketChannel channel]}]
                  (start-strike-ws-loop! channel strike-atom))}}))
 
-(defn- latest-price-handler [{:keys [binance frankfurter]} _req]
+(defn- latest-price-handler [{:keys [binance frankfurter query-fn]} _req]
   (let [price-atom (:latest-price binance)
         rates-atom (:rates frankfurter)
-        v          @price-atom]
+        v          (or @price-atom
+                       (when-let [row (query-fn :get-latest-binance-price {})]
+                         {:price       (:price row)
+                          :prev-price  (:price row)
+                          :recorded-at (:recorded_at row)}))]
     (if v
       {:status  200
        :headers {"Content-Type" "application/json"}