feat(auth): a password with TOTP on the register, and resets

The register's side of signing in with an address, a password that never
leaves the device (SRP-6a) and a code from an authenticator (ADR 0017),
with members forwarding every step through AccountRegister:

- password.set: salt, Argon2id's costs, SRP's verifier, the public keys
  and the private keys wrapped twice, all made on the device; with the
  address a mailed code proves, an anonymous person becomes identified
  under their ID. It signs in once an authenticator is confirmed.
- passwordSignIn.begin and complete: SRP's two steps with a TOTP or
  recovery code. An address nobody has is answered from a decoy key as
  an account would be; every wrong credential is refused alike.
- authenticator: secrets sealed under totpKey (XChaCha20-Poly1305, bound
  to their row), each code accepted once, ten recovery codes with the
  first, the last one kept.
- accountRecovery: a lost authenticator reset 72 hours after the
  password and a mailed code or the recovery phrase ask, a lost password
  set anew with the phrase's signature, or the account reset with new
  keys 72 hours after a mailed code asks; a mail at each start, a
  sign-in calling it off.
- An account with a password no longer signs in by a mailed code or
  GitHub; no new GitHub account is linked where passwords are offered,
  and from GITHUB_SIGN_IN_ENDS GitHub signs nobody in and its IDs go.

Five tables, added by the module's migration; deletePerson deletes
their rows.

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

packages/halkyon_base_server/pubspec.yaml

@@ -1,9 +1,9 @@
 name: halkyon_base_server
 description: >-
   What every Halkyon server has, as a Serverpod module: signing in
-  (anonymous, GitHub, a code by mail), the account's ways in and its
-  deletion, the pruning of what nobody can return to, and the instance's
-  basics.
+  (anonymous, a password with TOTP, a code by mail, GitHub), getting back
+  into an account, the account's ways in and its deletion, the pruning of
+  what nobody can return to, and the instance's basics.
 version: 0.1.0
 publish_to: none
 
@@ -15,6 +15,11 @@ resolution: workspace
 dependencies:
   clock: ^1.1.3
   crypto: ^3.0.7
+  # Pure Dart XChaCha20-Poly1305, which keeps TOTP secrets under the
+  # instance's key, and Ed25519, which checks a recovery phrase's proof (ADR
+  # 0017): what a server needs of both, without libsodium. Pinned exactly, as
+  # what keeps secrets must never move by accident.
+  cryptography: 2.9.0
   # Reads the pages profile links point to, for their rel="me" back-links.
   html: ^0.15.6
   # Asks the instance's register, and tells its members (ADR 0016).