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/session.svelte.ts

@@ -9,6 +9,7 @@
 import { fetchMe, tryRefresh } from '$lib/api/endpoints/auth';
 import { drives } from '$lib/stores/drives.svelte';
 import type { User } from '$lib/api/types';
+import { ensureActiveUser } from '$lib/utils/localStoragePrefs';
 
 class SessionStore {
 	user = $state<User | null>(null);
@@ -32,7 +33,8 @@ class SessionStore {
 			if (!me && (await tryRefresh())) {
 				me = await fetchMe();
 			}
-			this.user = me;
+			if (me) this.setUser(me);
+			else this.user = null;
 		} catch {
 			this.user = null;
 		}
@@ -40,6 +42,19 @@ class SessionStore {
 		return this.user;
 	}
 
+	/**
+	 * Set the authenticated user AND run per-user localStorage cleanup
+	 * (see `$lib/utils/localStoragePrefs::ensureActiveUser`). Direct
+	 * `session.user = …` assignments skip the cleanup — always call
+	 * `setUser` on login-flow entry points (form login, OIDC exchange,
+	 * existing-session probe) so a switch-account flow inside the same
+	 * tab observes the wipe.
+	 */
+	setUser(user: User): void {
+		this.user = user;
+		ensureActiveUser(user.id);
+	}
+
 	/**
 	 * Re-fetch the authenticated user from the server, bypassing the one-shot
 	 * `load()` cache. Call after operations that change server-side user state —