fix(legend): restore missing red color in outbreak probability legend

[evulins]

Description

Problem

The "Outbreak Probability" legend showed only 5 colors instead of 6 — the red
(15-25% "High") was missing and the last category "40-100% (Extreme)" rendered
as a blank box. The map itself colored correctly.

Cause

The legend used its own duplicated colors array that had drifted out of sync
with the map's palette in utils/colors.js. The #D95557 (red) entry was
missing, so with 5 colors for 6 thresholds every category shifted one slot and
"Extreme" was left with no color.

Fix

Re-export colors from utils/colors.js so the legend and the map share a
single source of truth and can't drift apart again.

Type of Change

• New feature
• Bug fix
• Breaking change
• Documentation update

Checklist

• Unit/integration tests
• Documentation

Tickets

• Issue Number

Screenshots

Please attach any design screenshots if UI update.

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