- [x] improve chrome cast subtitle rendering
    - native WebVTT style: white sans-serif, black outline, transparent background; physical-TV font-scale tuning remains unverified
- [x] currently, computer falls asleep even if video is playing. this should not be the case.
    - native playback activity prevents idle system sleep; local video keeps the display awake, casting allows screensaver/display sleep; native assertion checks and loopback Cast transitions passed, physical idle-TV verification remains unverified
- [x] add session-only local-file playlist support
    - multi-file Open/Finder/drop, natural filename order, editable queue sidebar, explicit append, previous/next and automatic advance; Cast navigation retains the receiver; UI/drag-drop and physical-Cast verification remain unverified
- [ ] in the "choose what to play" screen, we should change the youtube button to general streaming
	- we can figure out the stream and how to handle it from the url (i.e. if youtube url, handle as youtube stream; if miruro url, handle accordingly)