fix(app): GitHub's refusals say why, and no hint adds GitHub where passwords are offered

Where an instance offers password sign-in, GitHub is added to nobody (ADR
0017, D2), yet the start screen still said "then add GitHub" after a GitHub
account nobody has, and every refusal but an unknown account read
"Couldn't sign in with GitHub." (the end-to-end test of 21 Oct).

- The gateway tells from one read of the basics whether GitHub signs in and
  whether it is added to people (`gitHubOffer`, in place of
  `gitHubClientId`); the GitHub bloc keeps it (`Ready.linking`) for the
  profile, with why an attempt failed (`Ready.problem`).
- The instance's `usePassword`, `deprecated` and `ended` become problems of
  their own (`gitHubSignInProblemOf`), worded by `gitHubProblemText` and on
  the start screen; an anonymous person refused a link is told the GitHub
  account is nobody's and offered the password instead.
- Where passwords are offered, the start screen offers an account to create
  in place of the app's hint on adding GitHub.

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/lib/l10n/halkyon_app_de.arb

@@ -50,6 +50,11 @@
   "startAnonymous": "Dein Fortschritt wird auf diesem Gerät gespeichert. Melde dich an, um ihn zu behalten.",
   "startGitHubFailed": "Anmeldung mit GitHub fehlgeschlagen.",
   "startNoGitHubAccount": "Noch kein Konto hier meldet sich mit diesem GitHub-Konto an.",
+  "gitHubCreateAccountInstead": "Erstelle stattdessen ein Konto mit deiner E-Mail-Adresse und einem Passwort.",
+  "gitHubNoAccountSetUpPassword": "Noch kein Konto hier meldet sich mit diesem GitHub-Konto an. Richte stattdessen ein Passwort ein, um deinen Fortschritt zu behalten.",
+  "gitHubUsePassword": "Dieses Konto meldet sich jetzt mit seiner E-Mail-Adresse und seinem Passwort an, nicht mehr mit GitHub.",
+  "gitHubDeprecated": "GitHub lässt sich nicht mehr als Anmeldeweg hinzufügen: Deine E-Mail-Adresse und dein Passwort sind es.",
+  "gitHubEnded": "Die Anmeldung mit GitHub ist auf dieser Instanz beendet.",
   "startOtherInstance": "Andere Instanz verwenden",
   "syncTitle": "Synchronisierung",
   "syncNow": "Jetzt synchronisieren",

packages/halkyon_app/lib/l10n/halkyon_app_en.arb

@@ -167,6 +167,17 @@
   "startAnonymous": "Progress is saved on this device. Sign in to keep it.",
   "startGitHubFailed": "Couldn't sign in with GitHub.",
   "startNoGitHubAccount": "No account here signs in with this GitHub account yet.",
+  "gitHubCreateAccountInstead": "Create an account with your email address and a password instead.",
+  "@gitHubCreateAccountInstead": {
+    "description": "Said after a GitHub account nobody on the instance signs in with, where people sign in with a password and GitHub is added to nobody (ADR 0017)."
+  },
+  "gitHubNoAccountSetUpPassword": "No account here signs in with this GitHub account yet. To keep your progress, set up a password instead.",
+  "@gitHubNoAccountSetUpPassword": {
+    "description": "An anonymous person signed in with a GitHub account nobody here has, where GitHub is added to nobody: the password set up below keeps their account."
+  },
+  "gitHubUsePassword": "This account signs in with its email address and password now, not with GitHub.",
+  "gitHubDeprecated": "GitHub can't be added as a way to sign in any more: your email address and password are.",
+  "gitHubEnded": "Sign-in with GitHub has ended on this instance.",
   "startOtherInstance": "Use another instance",
   "syncTitle": "Sync",
   "syncNow": "Sync now",

packages/halkyon_app/lib/l10n/halkyon_app_localizations.dart

@@ -403,6 +403,36 @@ abstract class HalkyonAppLocalizations {
   /// **'No account here signs in with this GitHub account yet.'**
   String get startNoGitHubAccount;
 
+  /// Said after a GitHub account nobody on the instance signs in with, where people sign in with a password and GitHub is added to nobody (ADR 0017).
+  ///
+  /// In en, this message translates to:
+  /// **'Create an account with your email address and a password instead.'**
+  String get gitHubCreateAccountInstead;
+
+  /// An anonymous person signed in with a GitHub account nobody here has, where GitHub is added to nobody: the password set up below keeps their account.
+  ///
+  /// In en, this message translates to:
+  /// **'No account here signs in with this GitHub account yet. To keep your progress, set up a password instead.'**
+  String get gitHubNoAccountSetUpPassword;
+
+  /// No description provided for @gitHubUsePassword.
+  ///
+  /// In en, this message translates to:
+  /// **'This account signs in with its email address and password now, not with GitHub.'**
+  String get gitHubUsePassword;
+
+  /// No description provided for @gitHubDeprecated.
+  ///
+  /// In en, this message translates to:
+  /// **'GitHub can\'t be added as a way to sign in any more: your email address and password are.'**
+  String get gitHubDeprecated;
+
+  /// No description provided for @gitHubEnded.
+  ///
+  /// In en, this message translates to:
+  /// **'Sign-in with GitHub has ended on this instance.'**
+  String get gitHubEnded;
+
   /// No description provided for @startOtherInstance.
   ///
   /// In en, this message translates to:

packages/halkyon_app/lib/l10n/halkyon_app_localizations_de.dart

@@ -195,6 +195,26 @@ class HalkyonAppLocalizationsDe extends HalkyonAppLocalizations {
   String get startNoGitHubAccount =>
       'Noch kein Konto hier meldet sich mit diesem GitHub-Konto an.';
 
+  @override
+  String get gitHubCreateAccountInstead =>
+      'Erstelle stattdessen ein Konto mit deiner E-Mail-Adresse und einem Passwort.';
+
+  @override
+  String get gitHubNoAccountSetUpPassword =>
+      'Noch kein Konto hier meldet sich mit diesem GitHub-Konto an. Richte stattdessen ein Passwort ein, um deinen Fortschritt zu behalten.';
+
+  @override
+  String get gitHubUsePassword =>
+      'Dieses Konto meldet sich jetzt mit seiner E-Mail-Adresse und seinem Passwort an, nicht mehr mit GitHub.';
+
+  @override
+  String get gitHubDeprecated =>
+      'GitHub lässt sich nicht mehr als Anmeldeweg hinzufügen: Deine E-Mail-Adresse und dein Passwort sind es.';
+
+  @override
+  String get gitHubEnded =>
+      'Die Anmeldung mit GitHub ist auf dieser Instanz beendet.';
+
   @override
   String get startOtherInstance => 'Andere Instanz verwenden';
 

packages/halkyon_app/lib/l10n/halkyon_app_localizations_en.dart

@@ -193,6 +193,25 @@ class HalkyonAppLocalizationsEn extends HalkyonAppLocalizations {
   String get startNoGitHubAccount =>
       'No account here signs in with this GitHub account yet.';
 
+  @override
+  String get gitHubCreateAccountInstead =>
+      'Create an account with your email address and a password instead.';
+
+  @override
+  String get gitHubNoAccountSetUpPassword =>
+      'No account here signs in with this GitHub account yet. To keep your progress, set up a password instead.';
+
+  @override
+  String get gitHubUsePassword =>
+      'This account signs in with its email address and password now, not with GitHub.';
+
+  @override
+  String get gitHubDeprecated =>
+      'GitHub can\'t be added as a way to sign in any more: your email address and password are.';
+
+  @override
+  String get gitHubEnded => 'Sign-in with GitHub has ended on this instance.';
+
   @override
   String get startOtherInstance => 'Use another instance';