feat(filename): add parseFilename utility with full-pattern-only matching

Supports four patterns: date_lastname_firstname and lastname_firstname_date,
both with ISO (YYYY-MM-DD) and compact (YYYYMMDD) date formats.
Returns dateIso, personName and a formatted suggestedTitle.
Partial matches are rejected — unrecognised filenames return {}.

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

frontend/src/lib/utils/filename.spec.ts

@@ -0,0 +1,85 @@
+import { describe, it, expect } from 'vitest';
+import { parseFilename, stripExtension } from './filename';
+
+describe('parseFilename', () => {
+	describe('YYYY-MM-DD_Lastname_Firstname pattern', () => {
+		it('extracts date and name', () => {
+			expect(parseFilename('1965-03-12_Mueller_Hans.pdf')).toEqual({
+				dateIso: '1965-03-12',
+				personName: 'Hans Mueller',
+				suggestedTitle: 'Hans Mueller (12.03.1965)'
+			});
+		});
+
+		it('handles umlauts in names', () => {
+			const result = parseFilename('2024-01-15_Müller_Jürgen.pdf');
+			expect(result.personName).toBe('Jürgen Müller');
+		});
+	});
+
+	describe('YYYYMMDD_Lastname_Firstname pattern', () => {
+		it('extracts date and name', () => {
+			expect(parseFilename('19650312_Mueller_Hans.pdf')).toEqual({
+				dateIso: '1965-03-12',
+				personName: 'Hans Mueller',
+				suggestedTitle: 'Hans Mueller (12.03.1965)'
+			});
+		});
+	});
+
+	describe('Lastname_Firstname_YYYY-MM-DD pattern', () => {
+		it('extracts date and name', () => {
+			expect(parseFilename('Mueller_Hans_1965-03-12.pdf')).toEqual({
+				dateIso: '1965-03-12',
+				personName: 'Hans Mueller',
+				suggestedTitle: 'Hans Mueller (12.03.1965)'
+			});
+		});
+	});
+
+	describe('Lastname_Firstname_YYYYMMDD pattern', () => {
+		it('extracts date and name', () => {
+			expect(parseFilename('Mueller_Hans_19650312.pdf')).toEqual({
+				dateIso: '1965-03-12',
+				personName: 'Hans Mueller',
+				suggestedTitle: 'Hans Mueller (12.03.1965)'
+			});
+		});
+	});
+
+	describe('non-matching filenames', () => {
+		it('returns empty for date-only filename', () => {
+			expect(parseFilename('1965-03-12.pdf')).toEqual({});
+		});
+
+		it('returns empty for name-only filename', () => {
+			expect(parseFilename('Mueller_Hans.pdf')).toEqual({});
+		});
+
+		it('returns empty for unstructured filename', () => {
+			expect(parseFilename('scan_001.pdf')).toEqual({});
+		});
+
+		it('returns empty for three name segments without date', () => {
+			expect(parseFilename('Mueller_Hans_Juergen.pdf')).toEqual({});
+		});
+
+		it('returns empty for filename without extension', () => {
+			expect(parseFilename('1965-03-12_Mueller_Hans')).toEqual({});
+		});
+	});
+});
+
+describe('stripExtension', () => {
+	it('removes the extension', () => {
+		expect(stripExtension('document.pdf')).toBe('document');
+	});
+
+	it('removes only the last extension', () => {
+		expect(stripExtension('archive.tar.gz')).toBe('archive.tar');
+	});
+
+	it('leaves names without extension unchanged', () => {
+		expect(stripExtension('nodotfile')).toBe('nodotfile');
+	});
+});