chore: prepare v0.7.0 release

Wallpaper controls (fit/alignment/opacity), shared widget components
(combobox/slider/toggle/spinner), icon geometry module, surface opacity
policy, and the backdrop layer fix so wallpaper opacity fades toward the
theme background instead of exposing the desktop behind the window.

nebula-completions/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "nebula-completions"
-version = "0.6.0"
+version = "0.7.0"
 edition.workspace = true
 
 [features]