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.

docs/configuration.md

@@ -68,9 +68,10 @@ appearance, wallpaper, motion, input, bindings, rules, layouts, displays,
 and login items take effect live. If a reload is invalid, Ferese reports the error
 and keeps the last working configuration.
 
-When the shell starts, it loads your configuration or, if no file exists, uses
-the defaults. An invalid file stops startup with an error message, leaving your
-configuration untouched.
+At login, Ferese loads your configuration or uses the built-in defaults if the
+file is missing or invalid. For an invalid file, it shows a notification once
+the desktop is ready and leaves the file untouched, so you can correct it to
+match the current schema and reload your settings.
 
 ```sh
 feresectl reload-config          # reload with error feedback