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.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();
+}