Summary

Closes #639

Brings active selection highlighting to SDUI schema trees used by extension database drivers (ClickHouse, DuckDB, etc.), matching native tree selection visual styling (_PgTreeRow).

Changes

1. SduiTreeBuilder (lib/core/sdui/sdui_tree_builder.dart):
   • Added selectedNodeId and isNodeSelected predicate parameters.
   • Wrapped node rows in material.AnimatedContainer with 120ms QueryaMotion.fast duration.
   • Applied active selection design tokens: subtle primary background tint (alpha: 0.12), primary border outline (alpha: 0.35), and semibold typography (w600).
2. _ExtensionConnectionTile (lib/features/connections/connections_panel_extension.dart):
   • Extracted selectedExtensionObject and selectedConnectionId from _ConnectionsTreeSelectionScope.
   • Forwarded isNodeSelected predicate matching active database and table/view names.
3. Tests (test/core/sdui/sdui_builders_test.dart):
   • Added widget tests validating active selection styling for selectedNodeId and isNodeSelected.