fix: keep push notifications working when a mailbox is shared with you

Stalwart refuses a push subscription's whole emailPush map as a
`forbidden` SetError when it names a mailbox shared by ACL (0.16.16 and
later, and 1.0), and 1.0 stops listing emailpush on such accounts. The
app narrowed the map on any `forbidden`, including a refused method
call, and put every account with folders in the first attempt, so 1.0
cost one refused call per install. Worse, a failed listing counted as
"the server has no subscription" and dropped the key of a working
registration, and any failed refresh - a network error, a timeout, rate
limiting - started a replacement.

- `jmap-result` gains `JMAPSetError` (a `JMAPMethodError` with the same
  name, carrying `properties`) and `isJMAPSetError`. `assertSetResult`
  throws it, so every refused object can be told apart from a refused
  call; existing `instanceof` checks and the outbox's name-based error
  classification are unchanged.
- The emailPush map holds the primary account and the accounts whose
  `accountCapabilities` list `urn:ietf:params:jmap:emailpush`, which
  leaves ACL shares out up front on 1.0. On 0.16.16-0.16.23 the refused
  map still narrows to the accounts that look owned, then to the
  primary account, but only on a `forbidden` SetError.
- A subscription ends only with a verified replacement, a user disable
  or the server's verdict: a failed listing aborts the run, and only a
  SetError on the refresh starts a replacement. Other failures leave
  the subscription and its key alone and the next run tries again.
- `forbidden` and `overQuota` read as plain text in settings and the
  onboarding prompt, and settings says that mailboxes others share
  don't send background notifications. New strings in all 27 languages.

src/components/settings/NotificationSettings.tsx

@@ -14,6 +14,7 @@ import { SettingsSection, SettingItem, ToggleSwitch } from './settings-section';
 import { radius, spacing, typography, type ThemePalette } from '../../theme/tokens';
 import { useColors } from '../../theme/colors';
 import { useAuthStore } from '../../stores/auth-store';
+import { useEmailStore } from '../../stores/email-store';
 import { useLocaleStore } from '../../stores/locale-store';
 import { useSettingsStore } from '../../stores/settings-store';
 import {
@@ -24,6 +25,7 @@ import {
   isPushSupported,
   isValidRelayUrl,
   listPushDevices,
+  mailAccountsWithoutPush,
   PushSetupError,
   readPushAccountIds,
   revokePushDevice,
@@ -143,6 +145,26 @@ export function NotificationSettings() {
     // eslint-disable-next-line react-hooks/exhaustive-deps
   }, [activeAccountId, supported]);
 
+  // Stalwart pushes only the user's own mailboxes and their groups', so
+  // mailboxes shared by other users stay silent in the background (they still
+  // update while the app is open). Say so instead of leaving users to wonder.
+  const mailboxes = useEmailStore((s) => s.mailboxes);
+  const [sharedWithoutPush, setSharedWithoutPush] = useState(false);
+  useEffect(() => {
+    if (!supported || !client) {
+      setSharedWithoutPush(false);
+      return;
+    }
+    let cancelled = false;
+    const accountIds = mailboxes.flatMap((m) => (m.isShared && m.accountId ? [m.accountId] : []));
+    // Re-read after each enable run too: it may have added refused accounts.
+    void mailAccountsWithoutPush(accountIds).then(
+      (ids) => { if (!cancelled) setSharedWithoutPush(ids.length > 0); },
+      () => undefined,
+    );
+    return () => { cancelled = true; };
+  }, [supported, client, mailboxes, pushStatus.kind]);
+
   const describeError = (error: unknown): string => {
     if (error instanceof PushSetupError) {
       const phase = PHASE_KEYS[error.phase];
@@ -284,6 +306,15 @@ export function NotificationSettings() {
           </View>
         </SettingItem>
 
+        {sharedWithoutPush && (
+          <Text style={styles.fieldDescription}>
+            {t(
+              'settings.notifications.push.shared_mailboxes_no_push',
+              "Mailboxes others share with you don't send background notifications.",
+            )}
+          </Text>
+        )}
+
         {upSupported && (
           <>
             <SettingItem