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>

apps/learn/halkyon_learn_flutter/lib/l10n/app_de.arb

@@ -470,7 +470,6 @@
   "profileSettingsTooltip": "Einstellungen",
   "profileIdentified": "Dein Fortschritt wird in deinem Konto gespeichert.",
   "profileSignInWays": "Anmeldewege",
-  "profileWayGitHub": "GitHub",
   "profileWayEmail": "E-Mail-Adresse",
   "profileWayLinked": "Meldet dich an",
   "publicProfileTitle": "Öffentliches Profil",

apps/learn/halkyon_learn_flutter/lib/l10n/app_en.arb

@@ -535,7 +535,6 @@
   "profileSettingsTooltip": "Settings",
   "profileIdentified": "Your progress is kept with your account.",
   "profileSignInWays": "Ways to sign in",
-  "profileWayGitHub": "GitHub",
   "profileWayEmail": "Email address",
   "profileWayLinked": "Signs you in",
   "publicProfileTitle": "Public profile",

apps/learn/halkyon_learn_flutter/lib/l10n/app_localizations.dart

@@ -2830,12 +2830,6 @@ abstract class AppLocalizations {
   /// **'Ways to sign in'**
   String get profileSignInWays;
 
-  /// No description provided for @profileWayGitHub.
-  ///
-  /// In en, this message translates to:
-  /// **'GitHub'**
-  String get profileWayGitHub;
-
   /// No description provided for @profileWayEmail.
   ///
   /// In en, this message translates to:

apps/learn/halkyon_learn_flutter/lib/l10n/app_localizations_de.dart

@@ -1718,9 +1718,6 @@ class AppLocalizationsDe extends AppLocalizations {
   @override
   String get profileSignInWays => 'Anmeldewege';
 
-  @override
-  String get profileWayGitHub => 'GitHub';
-
   @override
   String get profileWayEmail => 'E-Mail-Adresse';
 

apps/learn/halkyon_learn_flutter/lib/l10n/app_localizations_en.dart

@@ -1702,9 +1702,6 @@ class AppLocalizationsEn extends AppLocalizations {
   @override
   String get profileSignInWays => 'Ways to sign in';
 
-  @override
-  String get profileWayGitHub => 'GitHub';
-
   @override
   String get profileWayEmail => 'Email address';
 

apps/learn/halkyon_learn_flutter/lib/src/core/dependencies/dependencies.dart

@@ -228,10 +228,6 @@ class Dependencies({
     final authGateway = ServerpodAuthGateway(
       client,
       base: client.modules.base,
-      // The scheme GitHub's sign-in returns to on Android, iOS and macOS, as
-      // each platform's project registers it for the app.
-      callbackScheme: 'app.halkyon.learn',
-      appName: 'Halkyon Learn',
     );
     final addresses = FileSignInAddresses(device.storage.peopleOf(instance));
     final accountCrypto = SodiumAccountCrypto();

apps/learn/halkyon_learn_flutter/lib/src/feature/auth/widget/profile_screen.dart

@@ -107,9 +107,8 @@ class const _Account() extends StatelessWidget {
   }
 }
 
-/// How the person signs in: GitHub where they have it (it is added to
-/// nobody any more, ADR 0020, D25), an email address, and SimpleLogin
-/// (D21), with the password and authenticators beneath.
+/// How the person signs in: an email address, and SimpleLogin (ADR 0020,
+/// D21), with the password and authenticators beneath.
 class const _SignInWays() extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
@@ -127,7 +126,6 @@ class const _SignInWays() extends StatelessWidget {
       children: [
         const SizedBox(height: 16),
         Text(l10n.profileSignInWays, style: theme.textTheme.titleSmall),
-        if (ways.ways.gitHub) way(l10n.profileWayGitHub, l10n.profileWayLinked),
         if (ways.ways.email)
           way(l10n.profileWayEmail, ways.emailAddress ?? l10n.profileWayLinked),
         // SimpleLogin (ADR 0020, D21): once added, one more way in here.