chore: Halkyon Learn moves into apps/learn

Its server, client, app and curator, and the tools that write its
assets (maps, Anki fixtures, icons), as they are; paths are fixed in
the commits that follow.

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/support/auth_fixtures.dart

@@ -0,0 +1,44 @@
+import 'package:halkyon_base_server/base.dart';
+import 'package:halkyon_learn_server/src/auth/learn_base.dart';
+import 'package:serverpod/serverpod.dart';
+import 'package:serverpod_auth_idp_server/core.dart';
+
+import '../test_tools/serverpod_test_tools.dart';
+
+/// Sets the server up as it runs (lib/server.dart): halkyon_base as Learn
+/// configures it (ADR 0014), so deleting a person deletes Learn's data of
+/// theirs too, and authentication. On the pod [sessionBuilder]'s sessions
+/// run on, not on `Serverpod.instance`: that is the pod made last, and a test
+/// file with several `withServerpod` groups has a pod each.
+void useLearnBase(TestSessionBuilder sessionBuilder) {
+  final pod = sessionBuilder.build().serverpod;
+  HalkyonBase.configure(pod, learnBase());
+  AuthServices.set(
+    tokenManagerBuilders: tokenManagerBuilders,
+    identityProviderBuilders: identityProviderBuilders(pod),
+  );
+}
+
+/// Signs [person] in on a new device and returns the new session's id.
+Future<UuidValue> signInNewDevice(
+  Session session,
+  UuidValue person, {
+  Set<Scope> scopes = const {},
+}) async {
+  Future<Set<UuidValue>> sessionIds() async => {
+    for (final serverSideSession in await ServerSideSession.db.find(
+      session,
+      where: (t) => t.authUserId.equals(person),
+    ))
+      serverSideSession.id!,
+  };
+
+  final before = await sessionIds();
+  await AuthServices.instance.tokenManager.createToken(
+    session,
+    authUserId: person,
+    method: 'test',
+    scopes: scopes,
+  );
+  return (await sessionIds()).difference(before).single;
+}

apps/learn/halkyon_learn_server/test/integration/support/sync_database.dart

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+import 'package:serverpod/serverpod.dart';
+import 'package:serverpod_offline_sync_server/serverpod_offline_sync_server.dart';
+
+/// The sync engine's database, as the running server has it, for
+/// `withServerpod(databaseInterceptor: …)`: deleted rows are tombstones it
+/// hides. Writing through it takes transactions of its own, outside the one
+/// a test would be rolled back in, so tests using it turn rollback off and
+/// delete what they made.
+Database syncDatabaseInterceptor(Session session, Database inner) {
+  final database = offlineSyncDatabaseInterceptor(session, inner);
+  if (database is OfflineSyncDatabase) {
+    _syncDatabases[session] = database;
+  }
+  return database;
+}
+
+/// The sync engine's database of each session, as the test pod's own
+/// database wraps it.
+final _syncDatabases = Expando<OfflineSyncDatabase>();
+
+/// Writes through [write] as [person] in their personal space, as their
+/// device would, on [session]'s sync engine database.
+Future<T> asPerson<T>(
+  Session session,
+  UuidValue person,
+  Future<T> Function(Transaction transaction) write,
+) => _syncDatabases[session]!.transactionForUser(person, write);