android: fix navigation bar always being bright even in dark mode (#3464)
Right now both light mode and dark mode get light navigation bar, and
looks jarring in the dark modes.
This commit applies a more appropriate color before the UI thread
runs (in app config), as well as applying the current theme background
after the UI shell is mounted.
This should fix #3332.
Co-authored-by: Hailey <me@haileyok.com>
authored by