Header: remove max-width constraint on mobile so header background
spans the full viewport width.
Theme: updateAdminConfig now applies the new theme immediately if
the user's current mode matches the changed side (e.g. changing
dark theme while in dark mode updates live, without page reload
or dark→light→dark toggle).
URL preview & playlist support:
- POST /url-info endpoint extracts metadata (title, type, entry count)
- Preview box shows playlist contents before downloading (up to 10 items)
- Auto-detect audio-only sources (SoundCloud, etc) and switch to Audio mode
- Video toggle grayed out for audio-only sources
- Enable playlist downloading (noplaylist=False)
Admin panel improvements:
- Expandable session rows show per-session job list with filename, size,
status, timestamp, and source URL link
- GET /admin/sessions/{id}/jobs endpoint for session job details
- Logout now redirects to home page instead of staying on login form
- Logo in header is clickable → navigates to home
UX polish:
- Tooltips on output format chips (explains Auto vs specific formats)
- Format tooltips change based on video/audio mode
