NeXroll v2.0.0-beta.4

A focused fix release for the v2 beta. Upgrade-safe: existing installs keep all data and settings.

Fixed

YouTube "Test Download" now actually works and tells you the truth. It was calling a yt-dlp command-line program that doesn't exist in the Docker image or the Windows build, so the test failed (and showed a confusing error) even when your cookies were perfectly valid. The test now:
- runs through the same download engine real trailer downloads use,
- checks a known-good control video to confirm your sign-in works, and
- lets you paste the specific trailer URL you're trying to download.
So instead of a vague failure, you'll see either "authentication is working" or "your cookies are stale" — and if a single trailer is the problem, "authentication is working, but that video is unavailable."
Browser-cookie downloads were silently broken (the option was passed to yt-dlp in the wrong format). Fixed. If you use an uploaded youtube_cookies.txt file, you were unaffected.
Clearer trailer errors — NeXroll now tells stale/missing cookies apart from a video that's simply private, removed, members-only, or age-restricted.
"This Week's Schedule" dashboard tile no longer cuts off the bottom of the week — it expands to show every active schedule.
The sidebar no longer drifts when you scroll a long page.

The loading screen now greets you with a rotating set of dry, theater-themed one-liners.

Feedback welcome - report anything odd on the issue tracker or Discord.