Stop duplicate push notifications and piling up subscriptions

Browsers subscribed to Email changes, so every read or move on any
client arrived as a push the worker could only show as "New mail". They
now subscribe to EmailDelivery, which changes only on delivery; Stalwart
sends a delivery to a subscription with an emailPush filter as an
EmailPush alone. The payload now names id and threadId, which Stalwart
sends only when asked, so notifications carry their actions and open the
message. The worker stays quiet while a focused window is open, and the
page leaves notifications to the worker where push is on.

Every renewal registered a new subscription, on the belief that a
repeated deviceClientId replaces the old one. Stalwart keeps both and
allows fifteen per account, which filled up. A browser now extends its
subscription, clears its own duplicates, replaces them only when its
endpoint changed, and on overQuota makes room among other browsers'
subscriptions. The server names its subscriptions by installation and
removes what its previous process registered, and extends rather than
re-creates.

Checked live on 0.16.22; the mock now keeps duplicates, enforces the
limit and accepts an expiry update.

Fixes #375.

KNOWN-ISSUES.md

@@ -48,6 +48,8 @@ works the same way — and dropped where 0.15 was the whole subject. Support for
 0.15 was removed on 2026-08-26; the last release that runs on it is tagged
 [`stalwart-0.15-support`](https://github.com/Coffey-Labs/ihasmail/releases/tag/stalwart-0.15-support).
 
+- **Push subscriptions are not replaced by a repeated `deviceClientId`, and an account holds fifteen.** ihasmail registered a new subscription on every renewal believing the old one would be replaced, as the mock did. **Confirmed live (0.16.22, 2026-09-16)**: a second create with the same `deviceClientId` leaves both in place, the sixteenth create is refused with `overQuota`, "There are too many subscriptions, please delete some before adding a new one.", and `update` of `expires` is accepted. `PushSubscription/get` does not return `url` (nor `keys`), so a subscription can only be matched by its `deviceClientId`. A `types` of `[]` or `null` is stored as *every* type, not none. Read from the 0.16.22 source: `EmailDelivery` changes only on delivery, a delivery reaches a subscription with an `emailPush` filter as an EmailPush alone, and the payload carries `id` and `threadId` only when they are named in `properties`. Browsers now subscribe to `EmailDelivery` only, extend rather than re-create, clear their own duplicates and make room on `overQuota`; the server removes what its previous process registered. The mock follows all of it ([#375](https://github.com/Coffey-Labs/ihasmail/issues/375)).
+
 - **Administration was built from Stalwart's source, and the first live run found the one thing the source reading got wrong.** Accounts and Domains were written on 2026-09-13 against the 0.16.22 source and a mock reproducing it, deployed the same day, and exercised against the live server from an administrator's session. On that server the Accounts list did not load: `x:Account/query` answered **`unsupportedFilter - type`**. A registry filter is keyed by the property's name *as it appears on the object*, and the discriminator is `@type`, so `{"type": "User"}` names nothing the server knows and fails the whole query; `{"@type": "User"}` is accepted. The research that fed the build had listed the field as `type`, and the mock took it without complaint — which is how it shipped. Fixed in [#336](https://github.com/Coffey-Labs/ihasmail/pull/336), and the mock now refuses any filter name the real server does not index, answering the way Stalwart does. Everything else was **confirmed live (2026-09-13)**, mostly read-only, with the domain writes made on a throwaway domain created for the purpose and removed afterwards:
 
   - **Permissions** come from `GET /api/account` in camelCase (`sysAccountGet`); an administrator's list held 641 of them and none were kebab-case, whatever the documentation shows. The menu gates on these.