feat(base)!: no anonymous accounts on the server (ADR 0020, D25)

The server's half of D25: every account has a way in, and the anonymous
accounts left from before go with the daily pruning.

- The module signs nobody in anonymously: `anonymousIdp` and
  `gitHubUpgrade` are gone, and so is linking GitHub at the register.
- A password is set only by someone whose address is theirs (a
  `firstPassword` code) or who signs in with GitHub alone (a fresh
  sign-in and a `signUp` code); an anonymous account is refused
  `wrongCredentials` before any code is used.
- SimpleLogin refuses to link onto a caller without `identified`
  (`wrongCaller`), the member's endpoint too, so nothing turns an
  anonymous account into one with a way in.
- `pruneAnonymousPeople` deletes every anonymous account left, however
  new, never one identified. Learn and Todo schedule it as
  `prune-accounts` and cancel the old `prune-abandoned-anonymous-people`
  entry once.
- Learn: someone without `identified` keeps no files;
  `FILE_LIMIT_ANONYMOUS_MB` is gone. `minimumAppBuild` is 23, as builds
  up to 22 start with an anonymous account.
- Learn's sync tests make their person and session by SQL in the
  development database, as Serverpod stores sessions.
- Docs, store listings and ADRs 0010, 0014, 0016, 0017 and 0019 amended.

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_server/test/integration/test_tools/serverpod_test_tools.dart

@@ -2008,13 +2008,11 @@ class _FilePruningFutureCall {
 }
 
 class _PruningFutureCall {
-  Future<void> pruneAnonymousPeople(
-    _ist.TestSessionBuilder sessionBuilder,
-  ) async {
+  Future<void> pruneAccounts(_ist.TestSessionBuilder sessionBuilder) async {
     var _localUniqueSession =
         (sessionBuilder as _ist.InternalTestSessionBuilder).internalBuild();
     try {
-      await _iip9210p.PruningPruneAnonymousPeopleFutureCall().invoke(
+      await _iip9210p.PruningPruneAccountsFutureCall().invoke(
         _localUniqueSession,
         null,
       );