fix(dashboard): summarise the whole window, not its newest bucket

[flyworker]

The reported problem

The 24-hour window showed the models from the last hour, not the last 24
hours. With nothing hovered the panel fell back to the newest bucket:

const activeIndex = hovered ?? (points.length > 0 ? points.length - 1 : null);

So the heading said "$0.1104 in this window" and the breakdown under it
described one hour of it. On this node six models earned over the day and only
two in the final hour, so four were missing from a panel that looked like it
described the day.

The panel now sums every interval in the window by default and labels itself
with the window it is showing. Hovering a bar still isolates that interval, and
the header says so rather than leaving it to be discovered.

The defect this uncovered

Summing the window made the segments disagree with the total. The per-model
split is rescaled onto the bucket total only when that total came from the
platform's ledger; a locally-priced bucket was left alone. But usd
differences the aggregate counter while the split differences each model's own
counter, and the two can disagree — a restart, or a model removed
mid-interval, leaves the per-model deltas summing above the aggregate one.
unattributed was clamped at zero, which hid the excess without removing it.

Looking at one bucket at a time concealed this. Looking at a window does not:

2026-09-04   usd=1.6396   models=2.3023   unattributed=0.5782

$2.30 of model segments drawn inside a $1.64 bar. The rescale now applies
whenever a split exceeds its own total, whichever produced that total.

Verification

Against this node's live data, the panel total now equals the header total for
every window, which it did not before:

window	header	segments now sum to
24h	$0.1105	$0.1105
7d	$19.1700	$19.1700
30d	$32.5816	$32.5816

The new test builds the counter disagreement directly and fails without the
backend change:

models 3.000000 + unattributed 0.000000 exceeds the bucket total 1.000000