fix(front): clean localStorage on user change

- fix issue with selected drive and user logout/login via another user
    (was raising a "404 not found")
    - normalize all localStorage to "oxi-" prefix
    - add a specific frontend/AGENTS.md for frontend part (stop increasing the global AGENTS.md)

frontend/src/lib/stores/files.svelte.ts

@@ -72,7 +72,7 @@ export type Section =
 	| 'photos'
 	| 'music';
 
-const VIEW_KEY = 'oxicloud_view_mode';
+const VIEW_KEY = 'oxi-view-mode';
 
 function readViewMode(): ViewMode {
 	if (typeof localStorage === 'undefined') return 'grid';