feat(auth): tell the user when the session expired

Every 401 from Auth or Core now goes through useSessionExpired: the login page
says the session expired and returns to the last page after login. App no
longer removes a token that only the browser clock calls expired, so a backend
401 is the one signal. A 403 on the profile now shows an error instead.

public/i18n/de.json

@@ -14,7 +14,8 @@
     "ERROR_PASSWORD": "Das Passwort darf nicht leer sein.",
     "ERROR_INVALID_CREDENTIALS": "E-Mail oder Passwort ist falsch.",
     "ERROR_TOO_MANY_ATTEMPTS": "Zu viele fehlgeschlagene Versuche. Bitte in {{minutes}} Minuten erneut versuchen.",
-    "ERROR_GENERIC": "Anmeldung fehlgeschlagen. Bitte später erneut versuchen."
+    "ERROR_GENERIC": "Anmeldung fehlgeschlagen. Bitte später erneut versuchen.",
+    "SESSION_EXPIRED": "Deine Sitzung ist abgelaufen. Bitte melde dich erneut an."
   },
   "REGISTRATION": {
     "TITLE": "Registrieren",

public/i18n/en.json

@@ -14,7 +14,8 @@
     "ERROR_PASSWORD": "The password must have at least one character.",
     "ERROR_INVALID_CREDENTIALS": "Email or password is wrong.",
     "ERROR_TOO_MANY_ATTEMPTS": "Too many failed attempts. Please try again in {{minutes}} minutes.",
-    "ERROR_GENERIC": "Login failed. Please try again later."
+    "ERROR_GENERIC": "Login failed. Please try again later.",
+    "SESSION_EXPIRED": "Your session has expired. Please log in again."
   },
   "REGISTRATION": {
     "TITLE": "Register",