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.ts

@@ -0,0 +1,56 @@
+import { isoToGerman } from './date';
+
+export interface FilenameParseResult {
+	/** ISO format: YYYY-MM-DD */
+	dateIso?: string;
+	/** "Firstname Lastname" — order reversed from filename convention */
+	personName?: string;
+	/** Ready-to-use title, e.g. "Hans Mueller (12.03.1965)" */
+	suggestedTitle?: string;
+}
+
+// Full-match patterns only. Name segments use Unicode letters (\p{L}) to cover umlauts etc.
+// Order: date_lastname_firstname
+const P_DATE_ISO_NAME = /^(\d{4}-\d{2}-\d{2})_(\p{L}+)_(\p{L}+)\.[^.]+$/u;
+const P_DATE_COMPACT_NAME = /^(\d{8})_(\p{L}+)_(\p{L}+)\.[^.]+$/u;
+// Order: lastname_firstname_date
+const P_NAME_DATE_ISO = /^(\p{L}+)_(\p{L}+)_(\d{4}-\d{2}-\d{2})\.[^.]+$/u;
+const P_NAME_DATE_COMPACT = /^(\p{L}+)_(\p{L}+)_(\d{8})\.[^.]+$/u;
+
+function compactToIso(compact: string): string {
+	return `${compact.slice(0, 4)}-${compact.slice(4, 6)}-${compact.slice(6, 8)}`;
+}
+
+export function parseFilename(filename: string): FilenameParseResult {
+	let dateIso: string;
+	let lastName: string;
+	let firstName: string;
+
+	let m: RegExpMatchArray | null;
+
+	if ((m = P_DATE_ISO_NAME.exec(filename))) {
+		[, dateIso, lastName, firstName] = m;
+	} else if ((m = P_DATE_COMPACT_NAME.exec(filename))) {
+		dateIso = compactToIso(m[1]);
+		lastName = m[2];
+		firstName = m[3];
+	} else if ((m = P_NAME_DATE_ISO.exec(filename))) {
+		lastName = m[1];
+		firstName = m[2];
+		dateIso = m[3];
+	} else if ((m = P_NAME_DATE_COMPACT.exec(filename))) {
+		lastName = m[1];
+		firstName = m[2];
+		dateIso = compactToIso(m[3]);
+	} else {
+		return {};
+	}
+
+	const personName = `${firstName} ${lastName}`;
+	const suggestedTitle = `${personName} (${isoToGerman(dateIso!)})`;
+	return { dateIso: dateIso!, personName, suggestedTitle };
+}
+
+export function stripExtension(filename: string): string {
+	return filename.replace(/\.[^/.]+$/, '');
+}