unlockDialog: Tweak lock screen when limit reached
Based on !3977 (merged)
Tweak apperance of lock screen when screen time limit is reached, so that the child cannot unlock, using the new MVP design as discussed at Teams/Design/os-mockups#271 (comment 2445908).
Can be tested with a GNOME OS demo image which also includes !3999 (merged).
The button is not part of this MR, see !3999 (merged).
Closes: #8577 (closed)
Edited by Ignacy Kuchciński
