fix: use Math.max for pyramid chart right-bar palette fallback

[fix2015]

Summary

Fixed incorrect palette color selection for the pyramid chart's right bar when the palette has 3 colors.

Changes

packages/flint-js/src/echarts/instantiate-spec.ts (line 1101)

Math.min(1, pal.length - 1) → Math.max(0, pal.length - 1)

When the palette has fewer than 4 colors, the fallback should select the last color. Math.min caps the index at 1, so a 3-color palette always picks pal[1] (the second color) instead of pal[2] (the last color):

Palette size	Math.min(1, len-1) (before)	Math.max(0, len-1) (after)
3 colors	pal[1] (wrong)	pal[2] (last — correct)
2 colors	pal[1] (last — ok)	pal[1] (last — ok)
1 color	pal[0] (only — ok)	pal[0] (only — ok)

Test plan

• Verified the fix selects the correct palette color for all palette sizes
• No change in behavior for palettes with 4+ colors (the pal[3] branch handles those)

[Chenglong-MS]

Very cool observation! This seems to be a special consideration for echarts?

For example, discrete schema