feat(bulk-upload): add bulkTitleFromFilename utility

Converts a raw filename into a human-readable title candidate by
stripping the extension and replacing underscore/hyphen runs with spaces.
Reuses the existing stripExtension() helper.

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

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

@@ -1,5 +1,5 @@
 import { describe, it, expect } from 'vitest';
-import { parseFilename, stripExtension } from './filename';
+import { parseFilename, stripExtension, bulkTitleFromFilename } from './filename';
 
 describe('parseFilename', () => {
 	describe('date-first patterns', () => {
@@ -86,6 +86,24 @@ describe('parseFilename', () => {
 	});
 });
 
+describe('bulkTitleFromFilename', () => {
+	it('replaces underscores with spaces', () => {
+		expect(bulkTitleFromFilename('hello_world.pdf')).toBe('hello world');
+	});
+
+	it('replaces hyphens with spaces', () => {
+		expect(bulkTitleFromFilename('2024-01-01_Max.pdf')).toBe('2024 01 01 Max');
+	});
+
+	it('collapses multiple separators', () => {
+		expect(bulkTitleFromFilename('foo__bar--baz.pdf')).toBe('foo bar baz');
+	});
+
+	it('strips extension', () => {
+		expect(bulkTitleFromFilename('document.pdf')).toBe('document');
+	});
+});
+
 describe('stripExtension', () => {
 	it('removes the extension', () => {
 		expect(stripExtension('document.pdf')).toBe('document');

frontend/src/lib/utils/filename.ts

@@ -81,3 +81,7 @@ export function parseFilename(filename: string): FilenameParseResult {
 export function stripExtension(filename: string): string {
 	return filename.replace(/\.[^/.]+$/, '');
 }
+
+export function bulkTitleFromFilename(filename: string): string {
+	return stripExtension(filename).replace(/[_-]+/g, ' ').trim();
+}