feat(base,app)!: GitHub signs nobody in any more (ADR 0020, D36)

Every account signs in with SimpleLogin or a password now, so GitHub
goes from the module, the shared app package, Learn and Todo, ahead of
ADR 0017's GITHUB_SIGN_IN_ENDS.

- halkyon_base: no `gitHubSignIn` endpoint, GitHub identity provider or
  GitHub refusals; no `githubClientId`/`githubClientSecret`, no
  `GITHUB_SIGN_IN_ENDS` and no `forgetGitHubAccounts`; the register
  loses `account-with-github`. `SignInWays.gitHub`, the basics'
  `gitHubClientId` and `gitHubSignInEnds`, and `PasswordRefusal`'s
  `signInAgain` and `noAddress` go. A first password takes a code
  mailed to the person's own address; an account without one sets none
  (`wrongCredentials`).
- Learn's server: `instance.info()` without `gitHubClientId`, the
  pruning without GitHub, and `minimumAppBuild` 24, as builds up to 23
  (v0.20.0) require `SignInWays.gitHub`: the server deploys with the
  release of build 24.
- halkyon_app: no GitHub button or problems on the start screen, no
  password offered after a GitHub sign-in, and `ServerpodAuthGateway`
  without the browser half only GitHub used (`(client, base:)`). The
  account section offers a first password only to an account with an
  address. `LoopbackWebAuth` and the apps' schemes stay, SimpleLogin's
  ways back.
- Learn's Profile lists no GitHub; the texts go (English, German).
- Serverpod's `serverpod_auth_idp_github_account` stays, as its
  migrations make it; a row goes with its account, and ADR 0020's D36
  gives operators the SQL to delete those left.
- deploy/: compose.yaml and .env.example without GitHub. The READMEs,
  AGENTS.md files and ADR 0017 amended.

BREAKING CHANGE: builds up to 23 can't read the instance's answers
about an account's ways in; minimumAppBuild is 24.

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

@@ -96,85 +96,8 @@ void main() {
     expect(gateway.accountDeletions, 0);
   });
 
-  test('signing in with GitHub from there switches to its person', () async {
-    start();
-    bloc.add(const SessionEventStarted());
-    await expectLater(bloc.stream, emits(const SessionStateSignedOut()));
-
-    bloc.add(const SessionEventGitHubRequested());
-
-    // A password is offered first (ADR 0017, D2), then the person's app.
-    const person = SignedIn(authUserId: 'github-person', isIdentified: true);
-    await expectLater(
-      bloc.stream,
-      emitsThrough(const SessionStateGitHubSignedIn(person)),
-    );
-    bloc.add(const SessionEventPasswordOfferDone());
-    await expectLater(bloc.stream, emits(const SessionStateActive(person)));
-  });
-
-  test('a GitHub account nobody here signs in with yet is said so; any '
-      'other refusal fails, and nothing is made either way', () async {
-    start();
-    bloc.add(const SessionEventStarted());
-    await expectLater(bloc.stream, emits(const SessionStateSignedOut()));
-
-    gateway.gitHubError = const GitHubSignInFailed(
-      GitHubSignInProblem.unknownAccount,
-    );
-    bloc.add(const SessionEventGitHubRequested());
-    await expectLater(
-      bloc.stream,
-      emitsInOrder([
-        const SessionStateSignedOut(busy: true),
-        const SessionStateSignedOut(problem: SignedOutProblem.noGitHubAccount),
-      ]),
-    );
-
-    gateway.gitHubError = const GitHubSignInFailed(GitHubSignInProblem.refused);
-    bloc.add(const SessionEventGitHubRequested());
-    await expectLater(
-      bloc.stream,
-      emitsInOrder([
-        const SessionStateSignedOut(busy: true),
-        const SessionStateSignedOut(problem: SignedOutProblem.failed),
-      ]),
-    );
-    expect(gateway.gitHubSwitches, 0);
-  });
-
-  test('an account that signs in with its password now, and GitHub having '
-      'ended, are each said so, signing nobody in', () async {
-    start();
-    bloc.add(const SessionEventStarted());
-    await expectLater(bloc.stream, emits(const SessionStateSignedOut()));
-
-    gateway.gitHubError = const GitHubSignInFailed(
-      GitHubSignInProblem.usePassword,
-    );
-    bloc.add(const SessionEventGitHubRequested());
-    await expectLater(
-      bloc.stream,
-      emitsInOrder([
-        const SessionStateSignedOut(busy: true),
-        const SessionStateSignedOut(problem: SignedOutProblem.usePassword),
-      ]),
-    );
-
-    gateway.gitHubError = const GitHubSignInFailed(GitHubSignInProblem.ended);
-    bloc.add(const SessionEventGitHubRequested());
-    await expectLater(
-      bloc.stream,
-      emitsInOrder([
-        const SessionStateSignedOut(busy: true),
-        const SessionStateSignedOut(problem: SignedOutProblem.gitHubEnded),
-      ]),
-    );
-    expect(gateway.gitHubSwitches, 0);
-  });
-
   test('a session the server ended asks how to start too', () async {
-    const stored = SignedIn(authUserId: 'github-1', isIdentified: true);
+    const stored = SignedIn(authUserId: 'person-1', isIdentified: true);
     start(status: stored);
     bloc.add(const SessionEventStarted());
     await expectLater(bloc.stream, emits(const SessionStateActive(stored)));
@@ -185,7 +108,7 @@ void main() {
   });
 
   test('deleting the account asks how to start', () async {
-    const stored = SignedIn(authUserId: 'github-1', isIdentified: true);
+    const stored = SignedIn(authUserId: 'person-1', isIdentified: true);
     start(status: stored);
     bloc.add(const SessionEventStarted());
     await expectLater(bloc.stream, emits(const SessionStateActive(stored)));
@@ -204,7 +127,7 @@ void main() {
 
   test('a deletion that fails keeps the person signed in, their app in '
       'place, and says so; asked again, it tries again', () async {
-    const stored = SignedIn(authUserId: 'github-1', isIdentified: true);
+    const stored = SignedIn(authUserId: 'person-1', isIdentified: true);
     start(status: stored);
     bloc.add(const SessionEventStarted());
     await expectLater(bloc.stream, emits(const SessionStateActive(stored)));
@@ -236,7 +159,7 @@ void main() {
 
   test('a sign-out that fails keeps the person signed in, their app in '
       'place, and says so', () async {
-    const stored = SignedIn(authUserId: 'github-1', isIdentified: true);
+    const stored = SignedIn(authUserId: 'person-1', isIdentified: true);
     start(status: stored);
     bloc.add(const SessionEventStarted());
     await expectLater(bloc.stream, emits(const SessionStateActive(stored)));