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>

scripts/docker-e2e.sh

@@ -0,0 +1,40 @@
+#!/usr/bin/env bash
+# Build the artifactapi container, bring up the full stack (postgres, redis,
+# minio, artifactapi) plus a static mock upstream, and run the dockerised e2e
+# suite against the running product over HTTP. Tears everything down on exit.
+set -euo pipefail
+
+cd "$(dirname "$0")/.."
+
+# Publish artifactapi on 8001 to avoid colliding with a local instance on 8000.
+export ARTIFACTAPI_PORT="${ARTIFACTAPI_PORT:-8001}"
+COMPOSE=(docker compose -f docker-compose.yml -f docker-compose.e2e.yml)
+API_URL="${ARTIFACTAPI_URL:-http://localhost:${ARTIFACTAPI_PORT}}"
+
+cleanup() {
+  echo "==> tearing down stack"
+  "${COMPOSE[@]}" down -v --remove-orphans >/dev/null 2>&1 || true
+}
+trap cleanup EXIT
+
+echo "==> building and starting stack (postgres, redis, minio, mockupstream, artifactapi)"
+"${COMPOSE[@]}" up -d --build postgres redis minio mockupstream artifactapi
+
+echo "==> waiting for artifactapi health at ${API_URL}"
+for i in $(seq 1 60); do
+  if curl -fsS "${API_URL}/health" >/dev/null 2>&1; then
+    echo "    healthy after ${i}s"
+    break
+  fi
+  if [ "$i" -eq 60 ]; then
+    echo "!!! artifactapi did not become healthy in time; recent logs:"
+    "${COMPOSE[@]}" logs --tail=50 artifactapi
+    exit 1
+  fi
+  sleep 1
+done
+
+echo "==> running dockerised e2e suite"
+ARTIFACTAPI_URL="${API_URL}" \
+MOCK_UPSTREAM_INTERNAL="${MOCK_UPSTREAM_INTERNAL:-http://mockupstream}" \
+  go test -tags=dockere2e -count=1 -timeout=10m -v ./e2e-docker/...