Add Kraken daily OHLC poller with database storage

Polls Kraken API for 1-day BTC/USD candles aligned to 00:01 UTC,
mirroring the existing hourly poller pattern.

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

resources/migrations/20260218100000-create-kraken-day.down.sql

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+DROP TABLE kraken_day;

resources/migrations/20260218100000-create-kraken-day.up.sql

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+CREATE TABLE kraken_day (
+  ts          BIGINT         NOT NULL PRIMARY KEY,
+  open        NUMERIC(18,8)  NOT NULL,
+  high        NUMERIC(18,8)  NOT NULL,
+  low         NUMERIC(18,8)  NOT NULL,
+  close       NUMERIC(18,8)  NOT NULL,
+  vwap        NUMERIC(18,8)  NOT NULL,
+  volume      NUMERIC(24,8)  NOT NULL,
+  trade_count INTEGER        NOT NULL,
+  created_at  TIMESTAMPTZ    NOT NULL DEFAULT NOW()
+);