- New ProxyDialog (Tools > Proxy Settings..., plus 'Proxy Settings...'
in the project panel and timeline Proxy submenus) unifying global
proxy settings, per-footage custom presets, generation and deletion
in one place instead of three scattered entry points; this also fixes
the Tools menu action opening the wrong preferences tab
- Preferences Disk tab gains an 'include audio in proxies' checkbox and
an ffmpeg executable path field (blank = auto-detect)
- Add ProxyDialog smoke tests
