ui: Mass layout refactor

- Replaced TabWidget mode selection with ComboBox
- Moved Timeline out of record/review widgets
- Added TimelineState struct
- Set slint style to cosmic

build.rs

@@ -1,3 +1,6 @@
 fn main() {
-    slint_build::compile("ui/app-window.slint").expect("Slint build failed");
+    let config = slint_build::CompilerConfiguration::new()
+        .with_style("cosmic".into());
+
+    slint_build::compile_with_config("ui/app-window.slint", config).expect("Slint build failed");
 }