refactor: convert relative imports to package imports

Replace all relative imports (../../) with package imports
(package:tatlock_ui/) across 29 files for cleaner, more
maintainable import paths.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

lib/shared/components/data_grid/widgets/data_grid_header.dart

@@ -1,7 +1,6 @@
 import 'package:flutter/material.dart';
-
-import '../data_grid_column.dart';
-import '../data_grid_config.dart';
+import 'package:tatlock_ui/shared/components/data_grid/data_grid_column.dart';
+import 'package:tatlock_ui/shared/components/data_grid/data_grid_config.dart';
 
 /// Header row for DataGrid.
 class DataGridHeader<T> extends StatelessWidget {