Withdraw the key manager, and keep what probing it established

A Settings section for public keys is furniture, not a feature. Nothing
in ihasmail signs, encrypts, decrypts or verifies with a key, so the
page could only ever tell the reader in its own footnote that adding one
does nothing. It is withdrawn on that reasoning -- the same reasoning
that closed PR #67, reached again with the code in front of us.

So this reverts every user-visible part of it: the section, the lib, the
mock handlers, the component and the 261 catalogue strings. Nothing in
web/ or server/ differs from main now.

What stays is the part that was expensive and is true regardless. The
x:PublicKey registry was probed against a live 0.16.20 on 2026-09-05,
and the findings are now in KNOWN-ISSUES rather than in a closed pull
request -- which is where they sat for the nine days between #67 and
this branch, and why the work was done twice. Consolidated into one
entry, framed as what Stalwart does rather than what ihasmail offers:

  - an ordinary user may read and write their own keys, whatever the
    permissions table says
  - the registry takes S/MIME certificates as well as OpenPGP keys, and
    parses both -- confirmed with a real self-signed X.509 certificate,
    and a malformed one gets its own BER decoding error
  - a key can parse and still be refused, with different words. A
    sign-and-certify key -- what `gpg --quick-generate-key` makes --
    gets "Could not find any suitable keys", which is not a paste error
    and must not be shown as one
  - emailAddresses comes back as {} when empty, an object where a list
    property should be an array. It type-checks, then throws in join()
  - a create answers with the id alone; patching `key` is allowed
  - expiresAt is the registry's field and is not derived from the key

ROADMAP now says plainly that key management has been built and
withdrawn twice, that the registry is not the obstacle, and that
verifying a signature -- which needs only public keys -- is the shortest
route to a key being worth having. Encryption at rest moves from "not
offered yet" to refused: it is a one-way door, since turning it off does
not decrypt what is already there, and that is not a switch to hand an
ordinary user however easy it would be to add.

web/src/locales/es.ts

@@ -1304,36 +1304,6 @@ export const catalog: Catalog = {
     "Empty “{name}”?": "¿Vaciar «{name}»?",
     "Delete them": "Eliminarlos",
     "Nothing was deleted": "No se ha eliminado nada",
-    // ── Encryption keys, over Stalwart's x:PublicKey registry (#67) ──
-    "Encryption keys": "Claves de cifrado",
-    "Not available on this server": "No disponible en este servidor",
-    "Public keys are kept in Stalwart's registry, which this server does not offer. ihasmail needs Stalwart 0.16 or newer for it.": "Las claves públicas se guardan en el registro de Stalwart, que este servidor no ofrece. ihasmail necesita Stalwart 0.16 o posterior para ello.",
-    "Public keys for this account — what other people encrypt to, and what a signature is checked against. These are public by nature: no private key is stored, requested, or sent by ihasmail.": "Claves públicas de esta cuenta: aquello con lo que otras personas cifran, y aquello con lo que se comprueba una firma. Son públicas por naturaleza: ihasmail no almacena, no solicita ni envía ninguna clave privada.",
-    "No keys yet": "Aún no hay claves",
-    "Add an OpenPGP public key or an S/MIME certificate to publish it on this account.": "Añada una clave pública OpenPGP o un certificado S/MIME para publicarlo en esta cuenta.",
-    "Key added": "Clave añadida",
-    "Key removed": "Clave quitada",
-    "Remove “{name}”?": "¿Quitar «{name}»?",
-    "this key": "esta clave",
-    "Anyone holding it can still use it — removing it here only stops this account offering it.": "Quien la tenga podrá seguir usándola: quitarla aquí solo hace que esta cuenta deje de ofrecerla.",
-    "Remove key": "Quitar clave",
-    "Key description": "Descripción de la clave",
-    "Untitled key": "Clave sin título",
-    "Click to rename": "Haga clic para cambiar el nombre",
-    "Expired": "Caducada",
-    "Added": "Añadida",
-    "Addresses": "Direcciones",
-    "No expiry set": "Sin caducidad establecida",
-    "Any address on this account": "Cualquier dirección de esta cuenta",
-    "cryptography\u0004Key": "Clave",
-    "Public key": "Clave pública",
-    "Work key": "Clave del trabajo",
-    "Paste the whole armoured block, headers included. The server checks it and says what is wrong if it cannot read it.": "Pegue el bloque blindado completo, cabeceras incluidas. El servidor lo comprueba y dice qué falla si no puede leerlo.",
-    "Add key": "Añadir clave",
-    "Add a key": "Añadir una clave",
-    "Stalwart stores these keys, and this release does no more than manage them: ihasmail does not yet sign, encrypt, decrypt or verify anything with them. Adding one does not by itself start encrypting your mail.": "Stalwart guarda estas claves y esta versión no hace más que gestionarlas: ihasmail todavía no firma, cifra, descifra ni verifica nada con ellas. Añadir una no empieza por sí sola a cifrar su correo.",
-    "Unrecognised": "No reconocida",
-    "No account to add a key to.": "No hay ninguna cuenta a la que añadir una clave.",
   },
   plurals: {
     // ── Third pass ─────────────────────────────────────────────────────