Clean up root directory: remove obsolete files, reorganize scripts

- Delete deprecated spec files (customtkinter, tkinter, old pyqt)
- Delete obsolete build scripts (replaced by justfile)
- Delete redundant README_BUILD.md (content in main README)
- Move generate_sample_data.py to scripts/ directory
- Update justfile to reference new script location

Author: alexander-vyh

README_BUILD.md

@@ -68,7 +68,7 @@ run-cli *ARGS:
 
 # Generate sample data
 generate-samples:
-    uv run python generate_sample_data.py
+    uv run python scripts/generate_sample_data.py
 
 # Run pre-commit hooks
 pre-commit: