Archive and mark read from the notification itself

Both happen in the background. The phone stays where it is.

This was twice described as impossible, here and in FEATURES.md: the
service worker was said to have no session, so anything touching mail had
to open the app. That is wrong, and checking it rather than repeating it
is the whole of this change. ihasmail's session is an httpOnly cookie
against its own origin and the only other thing the API asks for is a
fixed `x-requested-with` header, which is not a secret and is not held
anywhere. A same-origin fetch from the worker carries the cookie like any
other. Confirmed against the mock: logging in with curl and then issuing
`Email/set` with nothing but that cookie and the static headers marked a
message read and moved it to Archive, HTTP 200. Nothing the tab holds in
memory is involved, because the API asks for none of it.

Two actions, because `maxActions` is two on Android and anything past it
is dropped without a word. Archive and Mark as read are the two worth
having: they are what somebody does to a notification they have already
read the whole of. Reply is not among them -- it would have to open the
app, which is what tapping the notification does already.

The worker still cannot reach a catalogue. It is plain JavaScript copied
into the build, outside the bundle, with no i18n and no idea which
mailbox is the archive. So the app writes both down in the same cache it
already uses for handoffs, and rewrites them whenever the language, the
account or the folder list changes. Where there is no such note -- between
installing this worker and next opening ihasmail -- the notification
appears with no buttons at all, rather than English ones over a mailbox
guessed by name. That also fixes two strings the worker had always shown
in English regardless: "New mail" and "(no subject)".

A session can be gone by the time a button is pressed. That comes back as
a refusal and the notification says so, rather than vanishing as though
it had worked. It does not open the app to recover: being interrupted is
what the button existed to avoid.

The two claims that were wrong are corrected rather than quietly deleted,
including the one about push renewal -- which still needs a tab, but for
a different reason than the one given. The reason is when the worker
runs, not what it may do: it wakes only for a push, and the push stops
when the subscription lapses.

Two new strings, in all nine catalogues.

web/src/locales/de.ts

@@ -892,6 +892,8 @@ export const catalog: Catalog = {
 
     // ── Composer status, calendar title ────────────────────────────────
     "New message": "Neue Nachricht",
+    "New mail": "Neue E-Mail",
+    "Could not do that — open ihasmail and try again": "Nicht möglich – öffnen Sie ihasmail und versuchen Sie es erneut",
     "Sending…": "Wird gesendet…",
     "Saving…": "Wird gespeichert…",
     "Error": "Fehler",