fix(player): cover the navigation bar area in fullscreen so the feed doesn't show behind the player

[Priveetee]

Context (bug report):

• [Bug][5.2.0-beta3] Full screen video bottom not covered due to fix for issue 2491 PipePipe#2517

Follow-up to the edge-to-edge work in #53.

Summary

In fullscreen the player did not cover the navigation-bar area, so a strip at the bottom showed the feed behind it (Shorts, landscape and Bilibili vertical videos). This makes the player bottom-sheet inset handling fullscreen-aware: the player covers the whole screen in fullscreen, while the collapsed mini player still stays above the nav bar.

Problem

The player bottom sheet used Material's paddingBottomSystemWindowInsets, which shrinks the sheet content by the system-bar insets and is not fullscreen-aware. In fullscreen the content stopped above the nav bar:

fragment_player_holder  [0,0][1080,2400]
video_item_detail       [0,0][1080,2148]   # 252px short -> feed visible in [2148,2400]

Changes

• activity_main.xml: drop app:paddingBottomSystemWindowInsets on the player holder.
• VideoDetailFragment: apply the status/navigation-bar insets manually and fullscreen-aware (holder padding + bottom-sheet peek): zero in fullscreen so the player fills the screen, the nav-bar inset otherwise so the mini player / detail stay above the bars.

Validation

Pixel 8 emulator (API 36), 3-button navigation: in fullscreen the player now covers the whole screen (no feed strip at the bottom); the collapsed mini player still sits above the nav bar.

[Priveetee]

Hope that now it won't be some other repercussion in other places 😭😭😭