fix: switch from docker to podman for Makefile and Gitea Actions workflow

Makefile

@@ -1,10 +1,14 @@
 ROC_VERSION ?= 0.0.0-alpha2
 REGISTRY ?= git.roo.lol/jbrechtel
+# Use podman by default; override with: make BUILD_CMD=docker
+BUILD_CMD ?= podman
+BUILD_FLAGS ?= -f Containerfile
 
 .PHONY: build-base build-dev build-ci build-all push-base push-dev push-ci push-all
 
 build-base:
-	docker build \
+	$(BUILD_CMD) build \
+		$(BUILD_FLAGS) \
 		--target base \
 		--build-arg ROC_VERSION=$(ROC_VERSION) \
 		-t $(REGISTRY)/roc-tools-base:$(ROC_VERSION) \
@@ -12,7 +16,8 @@ build-base:
 		.
 
 build-dev:
-	docker build \
+	$(BUILD_CMD) build \
+		$(BUILD_FLAGS) \
 		--target dev \
 		--build-arg ROC_VERSION=$(ROC_VERSION) \
 		-t $(REGISTRY)/roc-tools-dev:$(ROC_VERSION) \
@@ -20,7 +25,8 @@ build-dev:
 		.
 
 build-ci:
-	docker build \
+	$(BUILD_CMD) build \
+		$(BUILD_FLAGS) \
 		--target ci \
 		--build-arg ROC_VERSION=$(ROC_VERSION) \
 		-t $(REGISTRY)/roc-tools-ci:$(ROC_VERSION) \
@@ -30,15 +36,15 @@ build-ci:
 build-all: build-base build-dev build-ci
 
 push-base:
-	docker push $(REGISTRY)/roc-tools-base:$(ROC_VERSION)
-	docker push $(REGISTRY)/roc-tools-base:latest
+	$(BUILD_CMD) push $(REGISTRY)/roc-tools-base:$(ROC_VERSION)
+	$(BUILD_CMD) push $(REGISTRY)/roc-tools-base:latest
 
 push-dev:
-	docker push $(REGISTRY)/roc-tools-dev:$(ROC_VERSION)
-	docker push $(REGISTRY)/roc-tools-dev:latest
+	$(BUILD_CMD) push $(REGISTRY)/roc-tools-dev:$(ROC_VERSION)
+	$(BUILD_CMD) push $(REGISTRY)/roc-tools-dev:latest
 
 push-ci:
-	docker push $(REGISTRY)/roc-tools-ci:$(ROC_VERSION)
-	docker push $(REGISTRY)/roc-tools-ci:latest
+	$(BUILD_CMD) push $(REGISTRY)/roc-tools-ci:$(ROC_VERSION)
+	$(BUILD_CMD) push $(REGISTRY)/roc-tools-ci:latest
 
 push-all: build-all push-base push-dev push-ci