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 It is withdrawn on that reasoning -- the same reasoning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withdrawn twice, that the registry is not the obstacle, and that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/uk.ts

@@ -1300,36 +1300,6 @@ export const catalog: Catalog = {
     "Empty “{name}”?": "Очистити «{name}»?",
     "Delete them": "Видалити їх",
     "Nothing was deleted": "Нічого не видалено",
-    // ── Encryption keys, over Stalwart's x:PublicKey registry (#67) ──
-    "Encryption keys": "Ключі шифрування",
-    "Not available on this server": "Недоступно на цьому сервері",
-    "Public keys are kept in Stalwart's registry, which this server does not offer. ihasmail needs Stalwart 0.16 or newer for it.": "Відкриті ключі зберігаються в реєстрі Stalwart, якого цей сервер не надає. Для цього ihasmail потребує Stalwart 0.16 або новішої версії.",
-    "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.": "Відкриті ключі цього облікового запису — те, чим інші шифрують листи для вас, і те, за чим перевіряється підпис. Вони відкриті за своєю природою: ihasmail не зберігає, не запитує і не надсилає закритих ключів.",
-    "No keys yet": "Ключів ще немає",
-    "Add an OpenPGP public key or an S/MIME certificate to publish it on this account.": "Додайте відкритий ключ OpenPGP або сертифікат S/MIME, щоб опублікувати його в цьому обліковому записі.",
-    "Key added": "Ключ додано",
-    "Key removed": "Ключ прибрано",
-    "Remove “{name}”?": "Прибрати «{name}»?",
-    "this key": "цей ключ",
-    "Anyone holding it can still use it — removing it here only stops this account offering it.": "У того, хто вже його має, він залишиться — тут це лише припиняє пропонувати його від цього облікового запису.",
-    "Remove key": "Прибрати ключ",
-    "Key description": "Опис ключа",
-    "Untitled key": "Ключ без назви",
-    "Click to rename": "Натисніть, щоб перейменувати",
-    "Expired": "Закінчився",
-    "Added": "Додано",
-    "Addresses": "Адреси",
-    "No expiry set": "Термін дії не задано",
-    "Any address on this account": "Будь-яка адреса цього облікового запису",
-    "cryptography\u0004Key": "Ключ",
-    "Public key": "Відкритий ключ",
-    "Work key": "Робочий ключ",
-    "Paste the whole armoured block, headers included. The server checks it and says what is wrong if it cannot read it.": "Вставте весь блок цілком, разом із заголовками. Сервер перевірить його і скаже, що не так, якщо не зможе прочитати.",
-    "Add key": "Додати ключ",
-    "Add a key": "Додати ключ",
-    "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 зберігає ці ключі, а ця версія лише керує ними: ihasmail поки нічого ними не підписує, не шифрує, не розшифровує і не перевіряє. Додавання ключа саме собою не починає шифрувати вашу пошту.",
-    "Unrecognised": "Не розпізнано",
-    "No account to add a key to.": "Немає облікового запису, до якого можна додати ключ.",
   },
   plurals: {
     // ── Third pass ─────────────────────────────────────────────────────