Add Makefile and refactor package structure

- Replace shell script with Makefile for build/install tasks
- Move main logic into main() function for proper packaging
- Configure package entrypoint in pyproject.toml

Makefile

@@ -0,0 +1,25 @@
+.PHONY: default venv build install clean
+
+default: install
+
+venv:
+	@[ ! -d ./venv ] && python3 -m venv venv && bash -c \
+		"source venv/bin/activate && \
+		pip install --upgrade pip && \
+		pip install -r requirements.txt" || true
+
+build: venv
+	@if [ -n "$$(git status --porcelain)" ]; then \
+		echo "[ERROR]: There are uncommitted changes or untracked files."; \
+		exit 1; \
+	fi
+	@bash -c \
+		"source venv/bin/activate && \
+		pip install build twine && \
+		python -m build"
+
+install: venv
+	@bash -c "source venv/bin/activate && pip install -e ."
+
+clean:
+	rm -rf venv dist tarc.egg-info