Move Python generation step into Docker, no local Python required

Add python3 and python3-yaml to the Docker image so generate_cards.py
runs inside the container. Both the generate and build-blanko Makefile
targets now use docker run instead of a local python3 call.
Remove Python/PyYAML from the README prerequisites.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Makefile

@@ -29,13 +29,16 @@ build-back: build-image
 	@echo "PDF generated: $(PDF_FILE_BACK)"
 
 # Generate all tex files from CSV + event.yml
-generate:
+generate: build-image
 	@echo "Generating cards from $(CSV_FILE) + event.yml..."
 	@if [ ! -f "$(CSV_FILE)" ]; then \
 		echo "Error: $(CSV_FILE) not found!"; \
 		exit 1; \
 	fi
-	python3 generate_cards.py
+	docker run --rm \
+		-v $(PWD):/workspace \
+		$(IMAGE_NAME) \
+		python3 generate_cards.py
 
 # Build personalized front + event back side PDFs
 build-personalized: generate build-image
@@ -55,7 +58,10 @@ build-personalized: generate build-image
 # Build blank (blanko) front + event back side PDFs (no CSV required)
 build-blanko: build-image
 	@echo "Generating blank card..."
-	python3 generate_cards.py --blanko
+	docker run --rm \
+		-v $(PWD):/workspace \
+		$(IMAGE_NAME) \
+		python3 generate_cards.py --blanko
 	@echo "Compiling blank front side to PDF..."
 	docker run --rm \
 		-v $(PWD):/workspace \