Fix progress bar calculation

[lukas-fichtner]

Hello there! This is my first Jellyfin PR – Feedback Welcome!

Changes

• Corrected condition to properly check if the current time is within the program's duration.
• Fixed progress percentage calculation using double division for accuracy.
• Replaced getPremiereDate() with getStartDate() for correct program start time.
• Refactored getRealTimeProgress() to ensure proper duration calculation.

Issues
Both Live TV progress bars are not working properly.
Couldn't find a matching issue, but this likely affects many. If one exists, please link it. Thanks!

[nielsvanvelzen]

Thanks! Seems like some of these slipped through in a migration I did some time ago 😅