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_client/lib/src/protocol/auth/device.dart

@@ -52,7 +52,8 @@ abstract class Device
   /// The session's id; signing the device out takes it.
   _isc.UuidValue sessionId;
 
-  /// How the session was started: "anonymous", "github" or "email".
+  /// How the session was started: "simplelogin" or "password", or for one
+  /// from before "email", "github" or "anonymous".
   String method;
 
   DateTime createdAt;

apps/learn/halkyon_learn_client/lib/src/protocol/client.dart

@@ -773,11 +773,10 @@ class EndpointInstance extends _isc.EndpointRef {
   @override
   String get name => 'instance';
 
-  /// This instance's offer: GitHub sign-in only with the operator's OAuth
-  /// app, email sign-in only where it can mail codes, where its source is,
-  /// the oldest app build it works with, the domain its people's handles
-  /// are on, the Jellyfin server it suggests, and
-  /// where it keeps people's data and its backups.
+  /// This instance's offer: email sign-in only where it can mail codes,
+  /// where its source is, the oldest app build it works with, the domain its
+  /// people's handles are on, the Jellyfin server it suggests, and where it
+  /// keeps people's data and its backups.
   _ida.Future<_i26u8vl4.InstanceInfo> info() =>
       caller.callServerEndpoint<_i26u8vl4.InstanceInfo>(
         'instance',

apps/learn/halkyon_learn_client/lib/src/protocol/instance/instance_info.dart

@@ -17,7 +17,6 @@ import 'package:serverpod_client/serverpod_client.dart' as _isc;
 abstract class InstanceInfo
     implements _isc.SerializableModel, _isc.ProtocolSerialization {
   InstanceInfo._({
-    this.gitHubClientId,
     required this.sourceCodeUrl,
     this.minimumAppBuild,
     this.accountDomain,
@@ -28,7 +27,6 @@ abstract class InstanceInfo
   });
 
   factory InstanceInfo({
-    String? gitHubClientId,
     required String sourceCodeUrl,
     int? minimumAppBuild,
     String? accountDomain,
@@ -40,7 +38,6 @@ abstract class InstanceInfo
 
   factory InstanceInfo.fromJson(Map<String, dynamic> jsonSerialization) {
     return InstanceInfo(
-      gitHubClientId: jsonSerialization['gitHubClientId'] as String?,
       sourceCodeUrl: jsonSerialization['sourceCodeUrl'] as String,
       minimumAppBuild: jsonSerialization['minimumAppBuild'] as int?,
       accountDomain: jsonSerialization['accountDomain'] as String?,
@@ -53,10 +50,6 @@ abstract class InstanceInfo
     );
   }
 
-  /// The client ID of this instance's GitHub OAuth app, or null when GitHub
-  /// sign-in is off here.
-  String? gitHubClientId;
-
   /// Where the source of what this instance runs is; the licences require
   /// offering it to the people who use it.
   String sourceCodeUrl;
@@ -96,7 +89,6 @@ abstract class InstanceInfo
   /// with some or all fields replaced by the given arguments.
   @_isc.useResult
   InstanceInfo copyWith({
-    String? gitHubClientId,
     String? sourceCodeUrl,
     int? minimumAppBuild,
     String? accountDomain,
@@ -109,7 +101,6 @@ abstract class InstanceInfo
   Map<String, dynamic> toJson() {
     return {
       '__className__': 'InstanceInfo',
-      if (gitHubClientId != null) 'gitHubClientId': gitHubClientId,
       'sourceCodeUrl': sourceCodeUrl,
       if (minimumAppBuild != null) 'minimumAppBuild': minimumAppBuild,
       if (accountDomain != null) 'accountDomain': accountDomain,
@@ -124,7 +115,6 @@ abstract class InstanceInfo
   Map<String, dynamic> toJsonForProtocol() {
     return {
       '__className__': 'InstanceInfo',
-      if (gitHubClientId != null) 'gitHubClientId': gitHubClientId,
       'sourceCodeUrl': sourceCodeUrl,
       if (minimumAppBuild != null) 'minimumAppBuild': minimumAppBuild,
       if (accountDomain != null) 'accountDomain': accountDomain,
@@ -145,7 +135,6 @@ class _Undefined {}
 
 class _InstanceInfoImpl extends InstanceInfo {
   _InstanceInfoImpl({
-    String? gitHubClientId,
     required String sourceCodeUrl,
     int? minimumAppBuild,
     String? accountDomain,
@@ -154,7 +143,6 @@ class _InstanceInfoImpl extends InstanceInfo {
     String? dataLocation,
     String? backupLocation,
   }) : super._(
-         gitHubClientId: gitHubClientId,
          sourceCodeUrl: sourceCodeUrl,
          minimumAppBuild: minimumAppBuild,
          accountDomain: accountDomain,
@@ -169,7 +157,6 @@ class _InstanceInfoImpl extends InstanceInfo {
   @_isc.useResult
   @override
   InstanceInfo copyWith({
-    Object? gitHubClientId = _Undefined,
     String? sourceCodeUrl,
     Object? minimumAppBuild = _Undefined,
     Object? accountDomain = _Undefined,
@@ -179,9 +166,6 @@ class _InstanceInfoImpl extends InstanceInfo {
     Object? backupLocation = _Undefined,
   }) {
     return InstanceInfo(
-      gitHubClientId: gitHubClientId is String?
-          ? gitHubClientId
-          : this.gitHubClientId,
       sourceCodeUrl: sourceCodeUrl ?? this.sourceCodeUrl,
       minimumAppBuild: minimumAppBuild is int?
           ? minimumAppBuild