fix: Undo button now correctly restores previous filter state instead of clearing all

Problem:
- Undo button (unfilter) was clearing all filters instead of restoring the previous state
- New HistoryManager system existed but wasn't used by FilterEngineTask
- Old database-based system deleted entries during undo, causing data loss
- If only one filter existed, complete unfilter occurred instead of restoration

Solution:
- Integrated HistoryManager into FilterEngineTask.execute_unfiltering()
- Pass history_manager through task_parameters for unfilter operations
- Rewritten execute_unfiltering() to use history.undo() for proper state restoration
- Direct filter application bypasses old database deletion logic

Benefits:
✓ Undo correctly restores previous filter expression
✓ Multiple undo/redo operations now work properly
✓ History preserved in memory (no database deletion)
✓ Better performance (no database access during undo)
✓ Consistent with modern history management pattern

Files modified:
- filter_mate_app.py: Pass history_manager in task_parameters (line ~520)
- modules/appTasks.py: Rewrite execute_unfiltering() (lines ~2955-3032)
- CHANGELOG.md: Document the fix

Note: Associated layers are cleared during undo. Future enhancement could
restore their filters too based on saved geometric relationships.
