refactor(base): SimpleLogin's forwarding page on the OpenID Connect module (ADR 0023)

halkyon_base depends on halkyon_oidc_server, and its forwarding page
is now the module's (`addOidcCallbackForwarding`) with Halkyon's table
of apps and its page in English or German; its tests keep what is
Halkyon's own, the rest is tested in the module.

Every host now includes the module: migrations `…-oidc-module` in
halkyon_base, Learn and Todo create its two tables (no data touched)
and record its version; Learn's devices get them empty, as they have
halkyon_base's server-only tables. halkyon_base_client depends on
halkyon_oidc_client, whose models its generated code uses, and Learn's
server image copies both packages into its narrowed workspace.

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_client/lib/migrations/migration_registry.dart

@@ -28,6 +28,7 @@ part '20261021100422048-session-ended-warning/migration.dart';
 part '20261021110159867-second-factor-paths/migration.dart';
 part '20261021134803749-reset-hold-outs/migration.dart';
 part '20261021184601197-private-studysets/migration.dart';
+part '20261023181810112-oidc-module/migration.dart';
 
 /// Migration registry for the client-side database.
 class MigrationRegistry {
@@ -58,6 +59,7 @@ class MigrationRegistry {
     _Migration20261021110159867_second_factor_paths(),
     _Migration20261021134803749_reset_hold_outs(),
     _Migration20261021184601197_private_studysets(),
+    _Migration20261023181810112_oidc_module(),
   ];
 
   /// List of all client-side database migration versions.