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>

packages/halkyon_base_server/test/integration/support/fixtures.dart

@@ -1,3 +1,4 @@
+import 'package:clock/clock.dart';
 import 'package:halkyon_base_server/base.dart';
 import 'package:halkyon_oidc_server/testing.dart';
 import 'package:serverpod/serverpod.dart';
@@ -102,7 +103,28 @@ Future<UuidValue> signInNewDevice(
   return (await sessionIds()).difference(before).single;
 }
 
-/// A person as an app's first launch creates them: anonymous.
+/// A person as codes by mail left them before passwords (ADR 0017):
+/// identified, with [address] as their only way in, and no password.
+Future<UuidValue> newPersonWithAddress(Session session, String address) async {
+  final person = (await AuthServices.instance.authUsers.create(
+    session,
+    scopes: {identified},
+  )).id;
+  // INSERT INTO "email_identity" ("authUserId", "addressHash", "createdAt")
+  //   VALUES ($1, $2, $3)
+  await EmailIdentity.db.insertRow(
+    session,
+    EmailIdentity(
+      authUserId: person,
+      addressHash: addressHash(session.serverpod, address),
+      createdAt: clock.now(),
+    ),
+  );
+  return person;
+}
+
+/// An anonymous account, as apps made them on their first start until
+/// ADR 0020, D25, left from before.
 Future<UuidValue> newAnonymousPerson(
   Session session, {
   DateTime? createdAt,