ui: Port to libadwaita

This ports the application to libadwaita, enabling us to use the libadwaita stylesheet and
widgets to better implement the Gnome Human Interface Guidelines.

Cargo.lock

@@ -499,7 +499,7 @@ name = "helvum"
 version = "0.4.1"
 dependencies = [
  "glib",
- "gtk4",
+ "libadwaita",
  "log",
  "once_cell",
  "pipewire",
@@ -527,6 +527,38 @@ version = "1.3.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "830d08ce1d1d941e6b30645f1a0eb5643013d835ce3779a5fc208261dbe10f55"
 
+[[package]]
+name = "libadwaita"
+version = "0.5.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "06444f4ca05a60693da6e9e2b591bd40a298e65a118a8d5e830771718b3e0253"
+dependencies = [
+ "gdk-pixbuf",
+ "gdk4",
+ "gio",
+ "glib",
+ "gtk4",
+ "libadwaita-sys",
+ "libc",
+ "pango",
+]
+
+[[package]]
+name = "libadwaita-sys"
+version = "0.5.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "021cfe3d1fcfa82411765a791f7e9b32f35dd98ce88d2e3fa10e7320f5cc8ce7"
+dependencies = [
+ "gdk4-sys",
+ "gio-sys",
+ "glib-sys",
+ "gobject-sys",
+ "gtk4-sys",
+ "libc",
+ "pango-sys",
+ "system-deps",
+]
+
 [[package]]
 name = "libc"
 version = "0.2.147"