Fix: stat cards render 24h counts as percentages

[mpont91]

The dashboard stat cards show things like "+10500% vs last period".

That number is not a percentage and there is no previous period. /api/stats returns plain counts:

countIf(ts >= now() - INTERVAL 1 DAY)              AS trades_24h,
uniqExactIf(proxy_address, ts >= now() - INTERVAL 1 DAY) AS traders_24h

and page.tsx passes them straight through:

trend={displayStats.trades_24h > 0 ? { value: displayStats.trades_24h, isPositive: true } : undefined}

while StatsCard appends a % and the caption "vs last period":

{trend.isPositive ? "+" : ""}{trend.value}%
...
<span>vs last period</span>

So 10,500 trades in the last day renders as "+10500%". On a fresh deployment the API makes it obvious — total_trades and trades_24h come back identical, which no percentage change could be:

{ "total_trades": 10500, "trades_24h": 10500 }

Adds isPercentage (off by default, so a count stays a count) and an optional label, and has the two call sites say "in the last 24h". Values are thousands-separated while we are here.

The component keeps rendering a real percentage the moment someone passes isPercentage: true, so nothing is lost if period-over-period comparison gets added later.

tsc --noEmit clean.