Update 3.12: Fixed regression where sidebar was not properly initialized on startup. Changes

Added a new color input to "Sidebar colors" in the Options page, allowing to set a custom color for sidebar icons; the original 7 predefined colors are now labeled "Classic icon color".
Fixed an issue with background feed monitoring where the alarm was not properly managed.
Fixed inconsistent time format display in the Options page.
Changed UI terminology from "Check feed" to "Refresh feed".
Revised several labels in the Options page for improved clarity and more accurate descriptions of their behavior.
Applied minor fixes, UI adjustments, and general code improvements.