Add real-time BTC price feed via Binance WebSocket

Connect to Binance trade stream, persist prices to binance_price table
(throttled to every 5s), and live-update the home page via HTMX polling.

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

resources/migrations/20260217000000-create-binance-price.down.sql

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

resources/migrations/20260217000000-create-binance-price.up.sql

@@ -0,0 +1,5 @@
+CREATE TABLE binance_price (
+  id          BIGSERIAL PRIMARY KEY,
+  price       NUMERIC(18,8) NOT NULL,
+  recorded_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);