- Introduced a `Dockerfile` for setting up a minimal Ubuntu-based build environment with required dependencies.
- Added `docker-build.sh` script to simplify Linux build and test execution using Docker or Podman.
- Updated `DEVELOPER_GUIDE.md` with instructions for using Docker/Podman for Linux builds, including CI/CD integration examples.
- 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.
