fix(charts): pie without legend, colours repeat, fixed radius #1160

Problem

• Pie radius is fixed at 100 px (quick_chart_view.dart:357): small on a large pane, clipped on a narrow one.
• No legend. Slice titles appear only for ≤ 8 slices, but up to 50 slices are drawn, coloured from 5 palette colours in a cycle, so colours repeat ten times. Slices cannot be identified.
• Slice titles use a fixed TextStyle(fontSize: 11) without colour, painted on top of the slice colour (contrast not guaranteed).

Scope

• Radius from the available size (LayoutBuilder), donut style consistent with the theme.
• Legend (right or below depending on width): colour, label, value, %; hover on a legend row highlights the slice and vice versa.
• Default Top 8 + Other (the shared Top N control from fix(charts): bar/line silently use the first 50 rows; add aggregation and Top N #1158), so colours do not repeat.
• Slice labels only as percentages for slices ≥ 5 %, colour chosen for contrast against the slice.

Acceptance

• With 30 categories: 8 slices + Other, all identifiable from the legend, no repeated colour.
• Pie fills the pane at 600 px and at 1 600 px wide without clipping.