- Implemented robust undo system supporting coalescing of text operations (insert, backspace, delete).
- Added `UndoSystem` integration into the editor/commands pipeline.
- Wrote extensive unit tests for various undo/redo scenarios, including multiline operations, cursor preservation, and history management.
- Refactored to ensure consistent cursor behavior during undo/redo actions.
- Updated CMake to include new tests.
- Introduced visual-line mode for multi-line selection and edits.
- Implemented commands, rendering, and keyboard shortcuts.
- Added tests for broadcast operations in visual-line mode.
- Removed standalone test executables (`test_undo`, `test_buffer_save`, `test_buffer_open_nonexistent_save`, etc.).
- Introduced `kte_tests` as a unified test runner.
- Migrated existing tests to a new minimal, reusable framework in `tests/Test.h`.
- Updated `CMakeLists.txt` to build a single `kte_tests` executable.
- Simplified dependencies, reducing the need for ncurses/GUI in test builds.
