fix(a11y): darken avatar palette teal for AA contrast against white

#007596 with white initials hits ~4.5:1 — at the AA threshold for
small text. #005F74 lifts it comfortably above 5:1, matching the
contrast margin of the other four palette entries.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/lib/shared/dashboard/ReaderPersonChips.svelte

@@ -2,7 +2,7 @@
 import type { components } from '$lib/generated/api';
 import * as m from '$lib/paraglide/messages.js';
 
-const AVATAR_PALETTE = ['#012851', '#5A3080', '#007596', '#2A6040', '#803020'] as const;
+const AVATAR_PALETTE = ['#012851', '#5A3080', '#005F74', '#2A6040', '#803020'] as const;
 function djb2(str: string): number {
 	let hash = 5381;
 	for (let i = 0; i < str.length; i++) hash = (hash * 33) ^ str.charCodeAt(i);