docs(adr): shared spaces, their screens in step 4

ADR 0044, D29 to D32: Share opens one sheet, people first, then the
community; a Viewer's studyset screen is read-only; a shared studyset
is marked with people; safety codes are compared from a member's row,
members matched to their keys by handle.

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_flutter/lib/src/feature/sharing/data/shared_space_gateway.dart

@@ -1,27 +0,0 @@
-import 'package:halkyon_base_client/halkyon_base_client.dart' as base;
-
-/// The shared spaces the instance keeps (halkyon_base's `sharedSpace`
-/// endpoint, Halkyon's ADR 0044, D1).
-abstract interface class SharedSpaceGateway() {
-  /// Makes a shared space holding a studyset, with the person its Owner;
-  /// returns its id, the sync engine's space.
-  Future<String> create();
-
-  /// Deletes [space] with everything in it; its Owner's.
-  Future<void> delete(String space);
-}
-
-/// [SharedSpaceGateway] on halkyon_base's `sharedSpace` endpoint.
-class ServerpodSharedSpaceGateway(final base.Caller _base)
-    implements SharedSpaceGateway {
-  /// What a Learn space holds, in the module's words for it.
-  static const kind = 'studyset';
-
-  @override
-  Future<String> create() async =>
-      (await _base.sharedSpace.create(kind)).id.uuid;
-
-  @override
-  Future<void> delete(String space) =>
-      _base.sharedSpace.delete(base.UuidValue.withValidation(space));
-}