Real volume bars in PriceChart histogram

[ozpool]

Problem

PriceChart.tsx feeds the volume histogram (bottom of chart) with Math.random() * 200 per tick. The bars look alive but mean nothing.

Proposal

Once #152 (candle store) lands, the volume field on each Candle is already populated. Drop the random call and read it directly:

volSeries.setData(candles.map(c => ({
  time: c.time,
  value: c.volume,
  color: c.close >= c.open ? "rgba(15, 165, 106, 0.45)" : "rgba(214, 48, 68, 0.45)",
})));

Live updates pick up volume from the same WS candle-update channel emitted by the bucket roll.

Acceptance

• Volume bars scale to actual fills.
• No bar appears in a minute with zero fills.

Depends on

#152