Add deposits read table (CQRS projection from bank_to_exchange events)

Project each bank_to_exchange event into a denormalized deposits table
with pre-computed EUR, DKK, and USD amounts using Frankfurter currency
rates. Replaces the aggregate get-deposit-totals query.

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

resources/migrations/20260308000000-create-deposits.up.sql

@@ -0,0 +1,12 @@
+CREATE TABLE deposits (
+  id          BIGSERIAL PRIMARY KEY,
+  event_id    BIGINT NOT NULL REFERENCES events(id) UNIQUE,
+  occurred_at TIMESTAMPTZ NOT NULL,
+  exchange    TEXT NOT NULL,
+  fiat_amount NUMERIC(18,2) NOT NULL,
+  fiat_currency TEXT NOT NULL,
+  amount_eur  NUMERIC(18,2),
+  amount_dkk  NUMERIC(18,2),
+  amount_usd  NUMERIC(18,2),
+  note        TEXT
+);