Recover from expired sessions and malformed requests in the dashboard

Three failure paths that ended at an English HTTP status line or at no
recovery at all:

An empty or non-numeric withdrawal amount parsed to NaN, which JSON.stringify
sends as null, which pydantic rejects with a 422 — and FastAPI's validation
errors use a list of field objects rather than the {code, message} shape, so
apiErrorMessage fell through to res.statusText and the user read
"Unprocessable Content". The amount is now checked before the request, and the
list shape maps to a translated "invalid request" as a backstop for any other
field that fails validation.

A token the server no longer accepts left the dashboard looking logged in
while every poll failed, re-toasting "session expired" indefinitely. call()
now logs out on that specific code, dropping back to the login form.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

app/static/i18n.js

@@ -130,6 +130,8 @@ const TRANSLATIONS = {
     'error.invalid_credentials': 'Wrong username or password.',
     'error.derivation_index_conflict': 'Registration failed, please try again.',
     'error.session_expired': 'Session expired, please log in again.',
+    'error.invalid_request': 'Invalid request, please check the entered data.',
+    'error.invalid_amount': 'Enter an amount greater than zero.',
 
     'loading.creating': 'Creating…',
     'loading.loggingIn': 'Logging in…',
@@ -260,6 +262,8 @@ const TRANSLATIONS = {
     'error.invalid_credentials': 'Username o password errati.',
     'error.derivation_index_conflict': 'Registrazione non riuscita, riprova.',
     'error.session_expired': 'Sessione scaduta, accedi di nuovo.',
+    'error.invalid_request': 'Richiesta non valida, controlla i dati inseriti.',
+    'error.invalid_amount': 'Inserisci un importo maggiore di zero.',
 
     'loading.creating': 'Creazione…',
     'loading.loggingIn': 'Accesso…',
@@ -390,6 +394,8 @@ const TRANSLATIONS = {
     'error.invalid_credentials': 'Usuario o contraseña incorrectos.',
     'error.derivation_index_conflict': 'No se pudo completar el registro, inténtalo de nuevo.',
     'error.session_expired': 'Sesión caducada, vuelve a iniciar sesión.',
+    'error.invalid_request': 'Solicitud no válida, revisa los datos introducidos.',
+    'error.invalid_amount': 'Introduce un importe mayor que cero.',
 
     'loading.creating': 'Creando…',
     'loading.loggingIn': 'Entrando…',
@@ -520,6 +526,8 @@ const TRANSLATIONS = {
     'error.invalid_credentials': "Nom d'utilisateur ou mot de passe incorrect.",
     'error.derivation_index_conflict': "L'inscription a échoué, veuillez réessayer.",
     'error.session_expired': 'Session expirée, veuillez vous reconnecter.',
+    'error.invalid_request': 'Requête invalide, vérifiez les données saisies.',
+    'error.invalid_amount': 'Saisissez un montant supérieur à zéro.',
 
     'loading.creating': 'Création…',
     'loading.loggingIn': 'Connexion…',
@@ -650,6 +658,8 @@ const TRANSLATIONS = {
     'error.invalid_credentials': 'Benutzername oder Passwort falsch.',
     'error.derivation_index_conflict': 'Registrierung fehlgeschlagen, bitte erneut versuchen.',
     'error.session_expired': 'Sitzung abgelaufen, bitte melde dich erneut an.',
+    'error.invalid_request': 'Ungültige Anfrage, bitte überprüfe die eingegebenen Daten.',
+    'error.invalid_amount': 'Gib einen Betrag größer als null ein.',
 
     'loading.creating': 'Wird erstellt…',
     'loading.loggingIn': 'Anmeldung…',
@@ -780,6 +790,8 @@ const TRANSLATIONS = {
     'error.invalid_credentials': 'Неверное имя пользователя или пароль.',
     'error.derivation_index_conflict': 'Не удалось завершить регистрацию, попробуйте ещё раз.',
     'error.session_expired': 'Сессия истекла, войдите снова.',
+    'error.invalid_request': 'Некорректный запрос, проверьте введённые данные.',
+    'error.invalid_amount': 'Введите сумму больше нуля.',
 
     'loading.creating': 'Создание…',
     'loading.loggingIn': 'Вход…',
@@ -910,6 +922,8 @@ const TRANSLATIONS = {
     'error.invalid_credentials': '用户名或密码错误。',
     'error.derivation_index_conflict': '注册失败，请重试。',
     'error.session_expired': '会话已过期，请重新登录。',
+    'error.invalid_request': '请求无效，请检查填写的内容。',
+    'error.invalid_amount': '请输入大于零的金额。',
 
     'loading.creating': '正在创建…',
     'loading.loggingIn': '正在登录…',