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/lib/server.dart

@@ -50,14 +50,17 @@ Future<void> run(List<String> args) async {
   // (decided 2026-10-13), so instance.info() can name it from the first ask.
   unawaited(JellyfinSuggestion.of(pod).look());
 
-  // Abandoned anonymous people are pruned daily (decided 2026-09-30).
-  // Scheduling always adds an entry, so the previous one goes first.
+  // The accounts nobody signs into any more, daily (decided 2026-09-30;
+  // every anonymous account left since ADR 0020, D25). Scheduling always
+  // adds an entry, so the previous one goes first, and the one scheduled
+  // under the earlier name, which would call nothing.
+  await pod.futureCalls.cancel(_anonymousPruning);
   await pod.futureCalls.cancel(_pruning);
   await pod.futureCalls
       .callRecurring(identifier: _pruning)
       .cron('17 3 * * *')
       .pruning
-      .pruneAnonymousPeople();
+      .pruneAccounts();
 
   // The IP addresses of sign-up attempts, hourly, once the rate limit is
   // done with them (decided 2026-10-10).
@@ -126,7 +129,10 @@ Future<void> _loadDictionaries(Serverpod pod) async {
 }
 
 /// The identifier of the daily pruning.
-const _pruning = 'prune-abandoned-anonymous-people';
+const _pruning = 'prune-accounts';
+
+/// The identifier the daily pruning had until ADR 0020, D25.
+const _anonymousPruning = 'prune-abandoned-anonymous-people';
 
 /// The identifier of the hourly forgetting of sign-up attempts.
 const _attemptPruning = 'forget-sign-up-attempts';