Rework, WinUI 3-compliant adjustments, fixes

* About:Firefox popup reworked – inspired by Fluver.
* Enforced the WinUI minimum window size.
* Extension panel font size increased.
* Fixed a 1px gap between horizontal tabs.
* Fixed overuse of the critical-only color in certain menus.
* Headers outside of menu flyouts now use the primary text color.
* Identity panel item size increased due to it being singular.
* Minor adjustment to the tab preview panel structure.
* Minor tweaks to vertical tabs.
* Progress styling for the side panel.
* Repositioned certain panels.
* Simplified tab preview panel animations to avoid unnecessary triggers and match WinUI flyouts.
* Some fixes for internal browser pages.

Author: Lockframe