Start with defaults when configuration is invalid (#29)

Invalid configuration currently prevents login. Ferese now starts with built-in defaults and shows a notification when the shell is ready, leaving the file untouched. Loading and validation belong to the config module, while the theme module resolves appearance. Validation remains strict, and failed live reloads keep the active settings.

The native Morph regression checks the animated input region and idle frame scheduling while its backing surface stays allocated.

Validation: workspace and Python tests, formatting, Clippy, release build, and isolated Wayland startup/reload and panel-motion tests. Native CI includes the startup regression.

Related: #28.

compositor/src/config.rs

@@ -2,6 +2,7 @@ mod appearance;
 mod bindings;
 mod input_motion;
 mod layout;
+mod loading;
 mod outputs;
 mod xwayland;
 
@@ -10,6 +11,7 @@ use std::error::Error;
 use std::fmt;
 use std::path::PathBuf;
 
+pub(crate) use self::loading::{prepare, prepare_document, read_source, startup};
 pub(crate) use self::xwayland::{XwaylandConfig, XwaylandStartup};
 use appearance::*;
 pub use appearance::{BorderGradient, FocusEffectSettings, MaterialStyle, ThemeSettings};
@@ -403,7 +405,7 @@ mod tests {
                     .contains("unknown field")
             );
             assert!(
-                crate::theme::prepare(&source, std::path::Path::new("/tmp"))
+                crate::config::prepare(&source, std::path::Path::new("/tmp"))
                     .err()
                     .unwrap()
                     .contains(&key.replace('-', "_"))