chore: use pipx in Makefile instead of pip

Makefile

@@ -1,14 +1,20 @@
 .PHONY: init test clean
 
+PIPX := $(shell command -v pipx --version 2> /dev/null)
 POETRY := $(shell command -v poetry 2> /dev/null)
 OTTERDOG_SCRIPT := $(realpath ./otterdog.sh)
 OTTERDOG_LINK := ~/.local/bin/otterdog
 
 init:
+ifndef PIPX
+	$(error "Please install pipx first, e.g. using 'apt install pipx'")
+endif
+
 ifndef POETRY
-	pip3 install "poetry==1.8.4"
-	poetry self add "poetry-dynamic-versioning[plugin]"
+	pipx install "poetry==1.8.4"
+	pipx inject poetry "poetry-dynamic-versioning[plugin]"
 endif
+
 	poetry config virtualenvs.in-project true
 	poetry install --only=main
 	poetry run playwright install firefox