test: comprehensive dockerised end-to-end suite (#97)

Adds a black-box e2e suite that runs against the **built container image** via docker-compose (complementing the in-process `e2e/` testcontainers suite).

## What it does
`make docker-e2e` → `scripts/docker-e2e.sh`: builds the image, brings up the full stack (postgres, redis, minio, artifactapi) plus a static nginx **mock upstream** for hermetic caching, waits for `/health`, runs `go test -tags=dockere2e ./e2e-docker/...`, and tears everything down.

## Coverage
- **Repository lifecycle** — add / change / delete for remote, local and virtual repos.
- **Caching** — one immutable artifact for **each of the 10 remote package types** (generic, docker, helm, pypi, npm, rpm, alpine, puppet, terraform, goproxy) proxied through the mock upstream: first fetch `X-Artifact-Source: remote`, second `cache`, bytes verified against the origin fixture.
- **Local uploads** — generic (upload/download), pypi (wheel + generated `simple/` index), rpm (real package + **automatic repodata** generation).
- **Virtual repositories** — pypi simple-index merge and helm `index.yaml` merge across two members.

## Notes
- The artifactapi host port is parameterised (`ARTIFACTAPI_PORT`, default `8000`; the e2e run uses `8001`) so it does not collide with a locally-running instance. This is the only change to the production `docker-compose.yml`.
- Fixtures under `e2e-docker/fixtures/` are real package files (incl. a real RPM so repodata parsing works); a `.gitignore` negation tracks them over the global ignore of those extensions.

## Validation
Ran `make docker-e2e` locally: **all suites pass** against the containerised product.

---------

Co-authored-by: BenVincent <benvin@main.unkin.net>
Reviewed-on: #97
Co-authored-by: Ben Vincent <ben@unkin.net>
Co-committed-by: Ben Vincent <ben@unkin.net>

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) .