feat(app): a lost password with the recovery phrase in SimpleLogin's sheet (ADR 0020, 7)

An account that signs in with SimpleLogin opens its keys with its
password. Where that is lost, the unlock step's "Forgot your password?"
opens one step: the recovery phrase, and a new password twice. There is
no address and no code: the SimpleLogin sign-in of a moment ago stands
for them (D20).

- The device opens the keys with the phrase (`keys.beginPhrase`) and
  wraps them under the new password (`AccountCrypto.newKeysPassword`).
  It then signs the phrase's proof bound to that password
  (`signKeysResetProof`), which `keys.resetPassword` takes with the
  sign-in. The keys stay, and every other session ends.
- A phrase that doesn't open the keys is refused on the device, and the
  instance gets no proof to count. Two passwords that differ are
  refused before anything is sent.
- The gateway's `beginPhrase` and `resetPassword` run on the account's
  own session, not yet the device's. The repository's `resetPassword`
  ties them together, and the cubit and sheet have their `forgot` step.
  Three texts are new, in English and German.
- halkyon_base_server exports `isKeysPassword` for the interop test,
  which checks against the register's checks, with real libsodium, what
  the device sends.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

docs/adr/0020-sign-in-with-simplelogin.md

@@ -107,6 +107,12 @@
   `removeProfile`, members asking it) empties the display name, bio, links and their
   checks and the avatar, keeps the row with its handle, and returns what is left; Learn's
   profile form starts afresh from it and offers no removing while nothing is filled in.
+  Then a lost password with the phrase (7, D20), in SimpleLogin's sheet: the unlock
+  step's Forgot your password? opens one step, the recovery phrase and a new password
+  twice, with no address or code, as the sign-in of a moment ago stands for them. The
+  device opens the keys with the phrase, wraps them under the new password and signs the
+  phrase's proof bound to it (`keys.beginPhrase`, `keys.resetPassword`); the keys stay,
+  every other session ends.
 - **Builds on:** ADR 0010 (email sign-in), ADR 0011 (profile pages), ADR 0016 (the
   register), ADR 0017 (a password, TOTP and the keys).
 - **Changes:** ADR 0017's way in on an instance that offers SimpleLogin (its keys, their