feat(redesign): token foundation close-out + design handoff (#854)

Adds the Mappe design handoff as in-repo ground truth and closes out the design-token foundation: --radius-sm/md/full + --shadow-sm/md tokens (distinct dark values in both dark blocks) and the canonical 10-color $lib/shared/avatarPalette.ts (AA-darkened sage/amber/sand swatches), guarded by avatarPalette.spec.ts. Closes #854.

frontend/src/lib/shared/avatarPalette.spec.ts

@@ -0,0 +1,50 @@
+import { describe, it, expect } from 'vitest';
+import { AVATAR_PALETTE } from './avatarPalette';
+
+// ─── WCAG 2.1 relative-luminance / contrast (1.4.3) ──────────────────────────
+// White initials sit on every palette color (DESIGN_RULES §5). The avatar
+// background is theme-invariant (same hex in light and dark), so a single
+// white-on-color check covers both themes.
+
+function srgbToLinear(channel: number): number {
+	const c = channel / 255;
+	return c <= 0.03928 ? c / 12.92 : Math.pow((c + 0.055) / 1.055, 2.4);
+}
+
+function relativeLuminance(hex: string): number {
+	const r = parseInt(hex.slice(1, 3), 16);
+	const g = parseInt(hex.slice(3, 5), 16);
+	const b = parseInt(hex.slice(5, 7), 16);
+	return 0.2126 * srgbToLinear(r) + 0.7152 * srgbToLinear(g) + 0.0722 * srgbToLinear(b);
+}
+
+function contrastRatio(a: string, b: string): number {
+	const la = relativeLuminance(a);
+	const lb = relativeLuminance(b);
+	const [hi, lo] = la > lb ? [la, lb] : [lb, la];
+	return (hi + 0.05) / (lo + 0.05);
+}
+
+const WHITE = '#ffffff';
+
+describe('AVATAR_PALETTE', () => {
+	it('has exactly 10 colors (DESIGN_RULES §5)', () => {
+		expect(AVATAR_PALETTE).toHaveLength(10);
+	});
+
+	it('is all lowercase 6-digit hex', () => {
+		for (const c of AVATAR_PALETTE) {
+			expect(c).toMatch(/^#[0-9a-f]{6}$/);
+		}
+	});
+
+	it('has no duplicate colors (each person color is distinct)', () => {
+		expect(new Set(AVATAR_PALETTE).size).toBe(AVATAR_PALETTE.length);
+	});
+
+	it('every color meets WCAG AA (>=4.5:1) against white initials in both themes', () => {
+		for (const c of AVATAR_PALETTE) {
+			expect(contrastRatio(c, WHITE)).toBeGreaterThanOrEqual(4.5);
+		}
+	});
+});

frontend/src/lib/shared/avatarPalette.ts

@@ -0,0 +1,32 @@
+/**
+ * Canonical 10-color person/avatar palette — single source of truth.
+ *
+ * Used by `<Avatar>` (issue #855), hashed by name so the same person renders the
+ * same color on every screen (DESIGN_RULES §5). Do not duplicate these values in
+ * CSS or another module; import this constant instead.
+ *
+ * White Montserrat initials sit on each color, so every swatch must meet WCAG AA
+ * (≥4.5:1) for normal text — avatar initials are 700-weight but ≤16px, below the
+ * large-text threshold. The background is theme-invariant (identical hex in light
+ * and dark, white initials in both), so one white-on-color check covers both
+ * themes. Guarded by `avatarPalette.spec.ts`.
+ *
+ * Three §1 brand hues failed white-on-color and use AA-darkened variants here;
+ * the bright originals remain the decorative tag-dot colors in `layout.css`
+ * (tag dots carry no text, so the contrast floor does not apply to them):
+ *   sage  #5a8a6a → #527e61  (3.98 → 4.65:1)
+ *   amber #c17a00 → #a46800  (3.47 → 4.61:1)
+ *   sand  #9a8040 → #897239  (3.79 → 4.64:1)
+ */
+export const AVATAR_PALETTE = [
+	'#527e61', // sage   (AA-adjusted from #5a8a6a)
+	'#a0522d', // sienna
+	'#a46800', // amber  (AA-adjusted from #c17a00)
+	'#607080', // slate
+	'#7a4f9a', // violet
+	'#c0446e', // rose
+	'#3060b0', // cobalt
+	'#4a7a3a', // moss
+	'#897239', // sand   (AA-adjusted from #9a8040)
+	'#c05540' // coral
+] as const;