feat(nosql): 1-click return to active Mongo collection and Redis key (#1024)

[ZhuchkaTriplesix]

Closes #1024

Summary

• MainScreenWorkspaceState: Track selectedRedisKey and lastSelectedRedisKey, updated restoreLastSelectedObject() to support both MongoDB collections and Redis keys alongside SQL tables.
• MongoStatsView: Added lastSelectedMongoCollection with fallback to lastSelectedMongoDb for OutlineButton(leading: Icon(Icons.table_chart_outlined), child: Text('Return to $collection')). Pinned header above body to avoid disappearing on loading/error states.
• MongoExplorerView: Preserves _lastSelectedCollection and passes it to MongoStatsView.
• RedisView: Added lastSelectedRedisKey with fallback to lastSelectedRedisDb for return button (Icons.vpn_key_outlined), wrapped actions in Wrap to prevent horizontal overflow, pinned header above body.
• RedisExplorerView: Preserves _lastSelectedKey across view transitions and passes it to RedisView. Added initialKey support.
• WorkspacePanel & MainScreen: Wired lastSelectedMongoCollection, selectedRedisKey, and lastSelectedRedisKey.
• Tests: Added full unit and widget test suite for NoSQL 1-click return to object (test/features/nosql/nosql_return_to_object_test.dart) and updated MainScreenWorkspaceStateTest.