Update Makefile target prerequisites

- Introduce new `check-ffmpeg` Makefile target to verify `ffmpeg` presence
- Refactor Makefile to use `check-ffmpeg` as a prerequisite for key build targets

Makefile

@@ -1,27 +1,31 @@
 VENV := . venv/bin/activate &&
 
 
+check-ffmpeg:
+ifeq (, $(shell which ffmpeg))
+	$(error "No ffmpeg in PATH, please install ffmpeg")
+else
+	@echo "ffmpeg is installed"
+endif
+
 freeze:
 	$(VENV) pip freeze > requirements.txt
 
 install:
-ifeq (, $(shell which ffmpeg))
-	$(error "No ffmpeg in PATH, please install ffmpeg")
-endif
 ifneq (, $(shell which asdf))
 	asdf install
 endif
 	python3 -m venv venv
 	$(VENV) pip install -r requirements.txt
 
-install-cli:
+install-cli: check-ffmpeg
 	pip install .
 
 test:
 	python -m unittest discover -s tests
 
-transcribe: install
+transcribe: install check-ffmpeg
 	$(VENV) python transcribe_me/main.py
 
-transcribe-install: install
+transcribe-install: install check-ffmpeg
 	$(VENV) python transcribe_me/main.py install