refactor(arch): eliminate reverse imports from lib/core into lib/features #1239

Problem

docs/architecture.md specifies a strict layering rule:

The dependency direction is features → core/shared, never the reverse.
core/ and shared/ must not import from features/.

Currently, lib/core/ contains several reverse dependencies into lib/features/:

1. Commands & Dialogs:
   lib/core/actions/querya_core_commands.dart imports dialogs from features:

   • features/connections/connection_creation_flow.dart
   • features/connections/team_profile_actions.dart
   • features/extensions/presentation/pages/extension_manager_dialog.dart
   • features/help/about_dialog.dart
   • features/onboarding/welcome_tour_dialog.dart
   • features/settings/preferences_dialog.dart
   • features/updater/update_dialog.dart

2. Extensions Command Sync:
   lib/core/extensions/extension_command_sync.dart imports:

   • features/extensions/extension_connection_picker_dialog.dart

3. MCP Query Service & Delegates:
   lib/core/mcp/mcp_query_service.dart and lib/core/mcp/mcp_sql_delegates.dart import:

   • features/erd/erd_catalog.dart
   • features/erd/erd_model.dart
   • features/workspace/sql_execution_delegate.dart
   • features/mysql/mysql_sql_workspace.dart
   • features/postgresql/postgres_sql_workspace.dart
   • features/sqlite/sqlite_sql_workspace.dart

4. SDUI Tree Builder:
   lib/core/sdui/sdui_tree_builder.dart imports:

   • features/connections/querya_connection_tree_row.dart

Scope

• Move top-level app action/command wiring (querya_core_commands.dart) to lib/app/ or introduce an action registration pattern where features register their own command handlers.
• Decouple MCP SQL execution delegates and ERD catalog models so that MCP in core/ does not depend on UI workspace classes.
• Move querya_connection_tree_row.dart model or interface to core/ or shared/ if needed by SDUI.
• Add an architectural check (or test) ensuring no features/ imports exist in lib/core/ and lib/shared/.

Acceptance

• git grep "import 'package:querya_desktop/features/" lib/core/ lib/shared/ returns 0 results.
• Existing functionality and tests remain green.