Add kraken_minute table with 15-second polling

1-minute OHLC candles from Kraken, polled every 15 seconds to keep the
in-progress candle fresh. Unlike hourly/daily pollers, this one keeps
the last candle and upserts it as it updates.

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

resources/migrations/20260313000000-create-kraken-minute.down.sql

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+DROP TABLE IF EXISTS kraken_minute;

resources/migrations/20260313000000-create-kraken-minute.up.sql

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+CREATE TABLE kraken_minute (
+  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()
+);