refactor(personFormat): replace getInitials(Person) with getInitials(name: string)

Unify the initials-extraction logic: the new string-based getInitials()
splits on whitespace, takes the first char of the first and last word
uppercased — matching the pattern that was already inlined in
CommentThread. Update PersonChip, DocumentMetadataDrawer, and
CommentThread to use the shared function.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/lib/components/CommentThread.svelte

@@ -5,6 +5,7 @@ import type { Comment } from '$lib/types';
 import MentionEditor from '$lib/components/MentionEditor.svelte';
 import { renderBody, extractContent } from '$lib/utils/mention';
 import { relativeTime } from '$lib/utils/time';
+import { getInitials } from '$lib/utils/personFormat';
 import type { MentionDTO } from '$lib/types';
 
 type Props = {
@@ -76,14 +77,6 @@ function isOwn(c: { authorId: string | null }): boolean {
 	return currentUserId !== null && c.authorId === currentUserId;
 }
 
-function getInitials(name: string): string {
-	return name
-		.split(/\s+/)
-		.slice(0, 2)
-		.map((w) => w.charAt(0).toUpperCase())
-		.join('');
-}
-
 function extractQuote(content: string): { quote: string | null; body: string } {
 	const match = content.match(/^>\s*"(.+?)"\s*\n\n?([\s\S]*)$/);
 	if (match) return { quote: match[1], body: match[2] };