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_app/test/auth/bloc/session_bloc_test.dart

@@ -154,25 +154,6 @@ void main() {
     expect(gateway.gitHubSwitches, 0);
   });
 
-  test('with an email address from there, it starts without an account and '
-      'asks for the address', () async {
-    start(signedOut: true);
-    bloc.add(const SessionEventStarted());
-    await expectLater(bloc.stream, emits(const SessionStateSignedOut()));
-
-    bloc.add(const SessionEventEmailRequested());
-
-    await expectLater(
-      bloc.stream,
-      emitsThrough(
-        const SessionStateActive(
-          SignedIn(authUserId: 'anonymous-1', isIdentified: false),
-          signsInWithEmail: true,
-        ),
-      ),
-    );
-  });
-
   test('a session the server ended asks how to start too', () async {
     const stored = SignedIn(authUserId: 'github-1', isIdentified: true);
     start(status: stored);