feat: add timeline navigation return to start functionality

- Add Enter key shortcut for seeking to timeline start (00:00:00)
- Add return to start button in timeline toolbar with skip-back icon
- Both methods complement existing Home key shortcut
- Update keyboard shortcuts help to display Enter key properly
- Maintain consistent UI styling with existing playback controls

Resolves #415

apps/web/src/hooks/use-keyboard-shortcuts-help.ts

@@ -77,6 +77,7 @@ const formatKey = (key: string): string => {
     .replace("down", "↓")
     .replace("space", "Space")
     .replace("home", "Home")
+    .replace("enter", "Enter")
     .replace("end", "End")
     .replace("delete", "Delete")
     .replace("backspace", "Backspace")