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/utils/personFormat.spec.ts

@@ -1,5 +1,6 @@
 import { describe, it, expect } from 'vitest';
 import {
+	getInitials,
 	abbreviateName,
 	formatXsMeta,
 	personAvatarColor,
@@ -8,6 +9,30 @@ import {
 	statusLabel
 } from './personFormat';
 
+// ─── getInitials ─────────────────────────────────────────────────────────────
+
+describe('getInitials', () => {
+	it('returns first chars of first and last word uppercased', () => {
+		expect(getInitials('Marcel Raddatz')).toBe('MR');
+	});
+
+	it('returns single char for a single-word name', () => {
+		expect(getInitials('Raddatz')).toBe('R');
+	});
+
+	it('returns empty string for an empty name', () => {
+		expect(getInitials('')).toBe('');
+	});
+
+	it('splits on whitespace only — hyphenated first word counts as one', () => {
+		expect(getInitials('Anna-Maria Raddatz')).toBe('AR');
+	});
+
+	it('ignores extra whitespace between words', () => {
+		expect(getInitials('  Karl   Raddatz  ')).toBe('KR');
+	});
+});
+
 // ─── abbreviateName ──────────────────────────────────────────────────────────
 
 describe('abbreviateName', () => {