Add event-sourced wallet and transaction tracking system

Wallets table with 7 seeded wallets, events table for three transaction
types (bank_to_exchange, exchange_to_wallet, wallet_to_wallet). Balances
computed from event credits/debits in sats. REST endpoints for CRUD.

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

resources/migrations/20260307100000-create-events.up.sql

@@ -0,0 +1,17 @@
+CREATE TABLE events (
+  id             BIGSERIAL PRIMARY KEY,
+  event_type     TEXT NOT NULL,
+  occurred_at    TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+  recorded_at    TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+  sats           BIGINT,
+  fee_sats       BIGINT,
+  fiat_amount    NUMERIC(18,2),
+  fiat_currency  TEXT,
+  from_wallet_id UUID REFERENCES wallets(id),
+  to_wallet_id   UUID REFERENCES wallets(id),
+  note           TEXT
+);
+--;;
+CREATE INDEX idx_events_type ON events (event_type);
+--;;
+CREATE INDEX idx_events_occurred ON events (occurred_at);