fix: update login screen, texture guide, background colors, divider

Description

update login screen to match new designs (add logo, update text strings, left-aligned, green, uppercase button text (on Android))
fix text input field background color https://github.com/techmatters/terraso-mobile-client/issues/688
in texture guide, move videos above questions and reduce question font size https://github.com/techmatters/terraso-mobile-client/issues/1535#issuecomment-2189430152
add divider to slope screen inputs https://github.com/techmatters/terraso-mobile-client/issues/1640