feat(auth)!: codes by mail no longer sign in

ADR 0017, step 3 (D4: nobody signs in with email codes yet, so the
password replaces them outright). `emailCode.verifyCode`,
`emailSignIn.signIn` and the switch token go, with the register's
`verifySignInCode` and `completeEmailSwitch` and their operations
between services. `emailCode.sendCode` stays, now without a session
(signing up and getting back in have none), as what proves an address
for a password's setup, a sign-up, a setup never finished and the
resets; `accountRecovery.sendCode`, which did that for the resets,
goes. The `switchChallengeId` column stays: Serverpod's challenges
still link a completion token, and older servers read it during a
deploy.

The apps: halkyon_app's email sign-in (its bloc, sheet, gateway calls
and the start screen's Continue with email) goes; Learn's profile and
Todo's account sheet show `AccountSecuritySection` (a password set up
by someone anonymous or signing in with GitHub, whose end it names;
the authenticators; changing the password; new recovery codes and
phrase), which reads anew after every change the repository makes.

BREAKING CHANGE: Learn's `minimumAppBuild` is 22: builds up to 21 sign
in with the endpoints that went. Todo was never released and stays at
build 1.

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/lib/src/register/instance_api.dart

@@ -178,20 +178,6 @@ Future<Map<String, Object?>?> _answer(
         network: arguments.string('network'),
       );
       return {'request': request.uuid};
-    case RegisterOperation.verifySignInCode:
-      final accepted = await register.verifySignInCode(
-        session,
-        person: arguments.id('person'),
-        request: arguments.id('request'),
-        code: arguments.string('code'),
-      );
-      return {'accepted': accepted.toJson()};
-    case RegisterOperation.completeEmailSwitch:
-      final account = await register.completeEmailSwitch(
-        session,
-        switchToken: arguments.string('switchToken'),
-      );
-      return {'account': account.uuid};
     case RegisterOperation.linkGitHub:
       await register.linkGitHub(
         session,