Match shell squircle outlines with compositor masks

Use shared corner geometry for shell controls, window clipping, materials and blur masks. Preserve circular pills and controls where appropriate, track contour changes in damage, and use tagged ferese-shape and libcosmic dependencies.

README.md

@@ -25,7 +25,7 @@ Ferese combines a window manager and desktop shell with one configuration.
 - [Continuum motion](docs/configuration.md#animations): interruptible springs, gesture momentum and motion settings shared by the compositor and shell
 - Multiple monitors with fractional scaling and automatic refresh-rate switching on low battery
 - Themes, wallpapers and blur that update live, with Light/Dark/Auto modes and custom KDL themes
-- Squircle window corners with matching borders and shadows
+- Squircle window and shell corners with matching borders, shadows and blur masks
 - Desktop widgets, including a clock and sticky notes
 - Screenshots with annotation, screen sharing and built-in recording
 - A built-in lock screen and authentication dialogs