Overview

This PR resolves two major sorting issues (closing #696):

1. Critical Data Grid Sorting Index Desync Fix: In VirtualResultGrid, in-memory sorting now preserves original model indices via _sortedToModelIndices. Staging buffer edits, deletions, and status checks now target the correct model row rather than the visual row index, eliminating silent data corruption during active sorting.
2. Interactive Server-Side Sorting in Table Views: Added interactive column headers with sort direction indicators (ASC / DESC) and safe quoted ORDER BY SQL generation to SqliteTableView, PostgresTableView, and MysqlTableView.

Key Changes

• VirtualResultGrid (lib/features/workspace/result_grid_view.dart):
  • Implemented sortResultGridRowsWithIndices returning SortedResultGridData with both sorted rows and sortedToModelIndices.
  • Maintained backward compatibility for sortResultGridRows.
  • Added _toModelRowIndex(visualRow) mapping in _VirtualResultGridState.
  • Forwarded modelRowIndex to _DataRow for stagingBuffer.getRowStatus, stagingBuffer.getCellStatus, setCell, setCellNull, revertCell, toggleDeleteRow, and revertRow.
• SqliteTableView (lib/features/sqlite/sqlite_table_view.dart):
  • Added interactive header cells cycling none -> ASC -> DESC -> none with arrow_upward_rounded / arrow_downward_rounded icons.
  • Parameterized _browseDataSql() with ORDER BY <quoted_column> ASC/DESC.
• PostgresTableView (lib/features/postgresql/postgres_table_view.dart):
  • Added interactive header sorting and parameterized _browseDataSql() with quotePostgresIdentifier.
• MysqlTableView (lib/features/mysql/mysql_table_view.dart):
  • Added interactive header sorting and parameterized _browseDataSql() with quoteMysqlIdentifier.
• Automated Tests:
  • test/features/workspace/result_grid_sorting_model_test.dart: Unit tests for index mapping and widget tests confirming staging mutations target the correct model row under active sorting.
  • test/features/workspace/table_view_sorting_test.dart: Unit tests for SQL generation across SQLite, PostgreSQL, and MySQL, plus widget tests for header interaction.

Verification

• flutter analyze: 0 issues found.
• All workspace and database test suites passed (425+ tests).

Closes #696