feat(meditate): Meditate's server, its sealed tables, and SimpleLogin's way back to it

halkyon_meditate_server and its generated client, copied from Todo's
and stripped to the module, the register and the sync engine (ADR 0038,
D1, D7): content_key, meditate_settings and sitting, synced and sealed,
each indexing spaceId and deleted with the person's space; two
migrations, the initial one and sittings (purely additive, the ADR
explains the SQL); ports 8280 to 8282 and PostgreSQL 8290 (D13).
Tests: the module's basics naming `meditate`, the sync engine refusing
calls without a session, the register's modes, and a person's deletion
taking their rows alone.

halkyon_base's forwarding page knows Meditate's ways back
(meditate-loopback on 43826, meditate-scheme app.halkyon.meditate),
which halkyon_app's repository names among the apps' ports.

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/meditate/halkyon_meditate_client/lib/migrations/migration_registry.dart

@@ -0,0 +1,19 @@
+/// AUTOGENERATED BY SERVERPOD create-migration - DO NOT EDIT BY HAND
+/// Merging: resolve registry conflicts the same as migration_registry.txt.
+library;
+
+import 'package:serverpod_database/serverpod_database.dart';
+
+part '20261103074902604-sittings/migration.dart';
+
+/// Migration registry for the client-side database.
+class MigrationRegistry {
+  /// Ordered list of all client-side database migrations.
+  /// New migrations are always appended at the end.
+  static final List<MigrationVersionSql> migrations = [
+    _Migration20261103074902604_sittings(),
+  ];
+
+  /// List of all client-side database migration versions.
+  static List<String> get versions => migrations.map((m) => m.version).toList();
+}