fix: guard formatDuration against NaN/Infinity input

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/main.ts

@@ -688,6 +688,7 @@ function parseDuration(duration: string): number {
 }
 
 function formatDuration(seconds: number): string {
+    if (!isFinite(seconds) || seconds < 0) return '00:00:00';
     const h = Math.floor(seconds / 3600);
     const m = Math.floor((seconds % 3600) / 60);
     const s = Math.floor(seconds % 60);
@@ -695,6 +696,7 @@ function formatDuration(seconds: number): string {
 }
 
 function formatDurationDashed(seconds: number): string {
+    if (!isFinite(seconds) || seconds < 0) return '00-00-00';
     const h = Math.floor(seconds / 3600);
     const m = Math.floor((seconds % 3600) / 60);
     const s = Math.floor(seconds % 60);