test: add comprehensive dockerised end-to-end suite

Add a black-box e2e suite (build tag dockere2e) that runs against the
built container image via docker-compose, plus a static nginx mock
upstream for hermetic caching tests.

Coverage:
- repository add/change/delete for remote, local and virtual repos
- caching (miss -> hit + byte integrity) for all 10 remote package types
- local uploads: generic, pypi (with generated simple index), rpm (with
  automatic repodata generation from a real package)
- virtual merges: pypi simple index and helm index.yaml

Driven by scripts/docker-e2e.sh (make docker-e2e): builds the image,
brings the stack up, waits for health, runs the suite, and tears down.
The artifactapi host port is parameterised (ARTIFACTAPI_PORT, default
8000; the e2e run uses 8001). Fixtures are force-tracked over the global
gitignore.

Makefile

@@ -1,4 +1,4 @@
-.PHONY: build test lint fmt e2e docker docker-ui compose clean tidy check-go
+.PHONY: build test lint fmt e2e docker-e2e docker docker-ui compose clean tidy check-go
 
 BINARY := bin/artifactapi
 MODULE := git.unkin.net/unkin/artifactapi
@@ -28,6 +28,11 @@ fmt: check-go
 e2e: check-go
 	TESTCONTAINERS_RYUK_DISABLED=true go test -tags=e2e -race -count=1 -timeout=5m ./e2e/...
 
+# Build the container, bring up the full docker-compose stack + a mock upstream,
+# and run the black-box suite against the running product.
+docker-e2e: check-go
+	./scripts/docker-e2e.sh
+
 docker:
 	docker build -t artifactapi:$(VERSION) .