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/lib/l10n/halkyon_app_en.arb

@@ -154,19 +154,6 @@
       }
     }
   },
-  "startWithGitHub": "Sign in with GitHub",
-  "startGitHubFailed": "Couldn't sign in with GitHub.",
-  "startNoGitHubAccount": "No account here signs in with this GitHub account.",
-  "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)."
-  },
-  "gitHubSimpleLoginInstead": "Continue with SimpleLogin to create one instead.",
-  "@gitHubSimpleLoginInstead": {
-    "description": "Said after a GitHub account nobody on the instance signs in with, where the instance offers SimpleLogin (ADR 0020): GitHub makes no account."
-  },
-  "gitHubUsePassword": "This account signs in with its email address and password now, not with GitHub.",
-  "gitHubEnded": "Sign-in with GitHub has ended on this instance.",
   "startOtherInstance": "Use another instance",
   "startNoWay": "{instance} offers no way to create an account.",
   "@startNoWay": {
@@ -229,14 +216,6 @@
   "syncMismatchMore": "More",
   "startSignIn": "Sign in",
   "startCreateAccount": "Create an account",
-  "startGitHubEnds": "Sign-in with GitHub ends on {date}.",
-  "@startGitHubEnds": {
-    "placeholders": {
-      "date": {
-        "type": "String"
-      }
-    }
-  },
   "passwordAddress": "Email address",
   "passwordPassword": "Password",
   "passwordNewPassword": "New password",
@@ -394,14 +373,6 @@
   },
   "passwordSectionTitle": "Password and authenticator",
   "passwordSectionFailed": "Couldn't read how your account signs in.",
-  "passwordSectionGitHubEnds": "Sign-in with GitHub ends on {date}. Set up a password before then to keep your account.",
-  "@passwordSectionGitHubEnds": {
-    "placeholders": {
-      "date": {
-        "type": "String"
-      }
-    }
-  },
   "passwordSectionSetUp": "Set up a password",
   "passwordSectionSetUpHint": "Sign in with your email address, a password and an authenticator app.",
   "passwordSectionUnfinished": "Finish setting up: add an authenticator",
@@ -446,7 +417,6 @@
   "passwordNoReset": "No reset waits for this address.",
   "passwordExists": "This address's account has a password already. Sign in with it, or get back in if you've forgotten it.",
   "passwordAddressTaken": "This address belongs to another account.",
-  "passwordNoAddress": "Your account has no email address yet.",
   "passwordNoPassword": "This account has no password.",
   "passwordWrongCode": "This code isn't right. Enter the one your app shows now.",
   "passwordLastAuthenticator": "Your last authenticator can't go: every sign-in needs one.",
@@ -498,11 +468,6 @@
   "passwordAddressUnknown": "Enter your account's email address: the code goes there.",
   "passwordDeleteIntroByMail": "Your account goes with everything in it, in every service of this instance. None of its authenticators works now, so a code by mail confirms it: type your password, then the code we email to your address.",
   "passwordDeleteSendCode": "Email me a code",
-  "passwordSignInAgain": "To give an account that signs in with GitHub its password, sign in with GitHub again first: it has been more than a few minutes.",
-  "passwordSignInWithGitHubAgain": "Sign in with GitHub again",
-  "passwordOfferTitle": "Set up a password",
-  "passwordOfferBody": "Sign-in with GitHub is ending. Set up a password and an authenticator app to keep your account.",
-  "passwordOfferLater": "Later",
   "passwordAuthenticatorPasswordIntro": "To add it, confirm it is you with your password.",
   "passwordWarningTitle": "Someone tried your password",
   "passwordWarningBody": "On {date}, a device signed in to your account sent a wrong password or code ten times in a row, and was signed out. If that wasn't you, someone else may have that device or its session: change your password.",
@@ -535,14 +500,6 @@
   "passwordResetsCallOff": "Call it off",
   "passwordCallOffTitle": "Call off the reset",
   "passwordCallOffIntro": "Your password and a code call off every reset waiting.",
-  "passwordSectionGitHubEndsDeletes": "Sign-in with GitHub ends on {date}. Set up a password before then: an account without one is deleted 30 days later, with everything in it.",
-  "@passwordSectionGitHubEndsDeletes": {
-    "placeholders": {
-      "date": {
-        "type": "String"
-      }
-    }
-  },
   "passwordSignedInBefore": "Only a device signed in since then can dismiss this warning: sign in again on this one, or change your password.",
   "simpleLoginContinue": "Continue with SimpleLogin",
   "simpleLoginNote": "SimpleLogin is Proton's sign-in, and a Proton account works there too. It learns that you use {instance}, which keeps only your SimpleLogin ID: your name suggests a handle once, and nothing else is kept.",