Add deposit totals API endpoint

GET /api/deposits/totals returns fiat deposited per exchange per currency
from bank_to_exchange events, aggregated via SQL.

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

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

@@ -172,7 +172,9 @@
     {:get (fn [req] (tx/get-wallet-events opts req))}]
    ["/events"
     {:get  (fn [req] (tx/list-events opts req))
-     :post (fn [req] (tx/create-event! opts req))}]])
+     :post (fn [req] (tx/create-event! opts req))}]
+   ["/deposits/totals"
+    {:get (fn [req] (tx/get-deposit-totals opts req))}]])
 
 (defn route-data [opts]
   (merge