Feat/v3 go rewrite (#47)

Complete rewrite of ArtifactAPI from Python/FastAPI to Go as a single binary.

Core engine:
- 10 package providers: generic, docker, helm, pypi, npm, rpm, alpine,
  puppet, terraform, goproxy — each with built-in mutable patterns
- Content-addressable storage (SHA256 dedup across all remotes)
- Three-tier caching: Redis (TTL/locks) → S3/MinIO (blobs) → upstream
- Classifier with allowlist/blocklist per-remote (empty = allow all)
- Circuit breaker, conditional revalidation, stale-on-error
- Background garbage collection for orphaned blobs
- Access logging to PostgreSQL

API:
- v1 proxy endpoints (backwards compatible)
- v2 management API: CRUD remotes/virtuals, object browser, stats,
  health, SSE events, probe/test endpoint
- Virtual repos with index merging (Helm YAML + PyPI HTML)

Frontend (React + Vite, separate Dockerfile):
- Dashboard with stats, health indicators, top remotes
- Remotes list with type filter, remote detail with config/patterns
- Object browser with pagination and evict
- Test Remote page: probe any remote path, see headers/size/timing
- Virtuals page with expandable member lists

TUI (Bubble Tea):
- Dashboard, remotes list/detail, object browser, virtuals
- Vim-style navigation, artifactapi tui --endpoint <url>

Infrastructure:
- S3 client supports MinIO, Ceph RGW, AWS S3 (minio-go)
- PostgreSQL schema with migrations
- Docker Compose: API + UI + Postgres 17 + Redis 7 + MinIO
- Makefile with Go version check, build/test/lint/fmt/e2e targets
- Distroless Docker image (~15MB)

Testing:
- Unit tests for models, classifier, providers, mergers
- E2E tests with testcontainers-go (real Postgres/Redis/MinIO)

Terraform config:
- All 40 production remotes + helm virtual as HCL
- Provider repo: terraform-provider-artifactapi v0.0.1 (separate)

---------

Co-authored-by: Ben Vincent <ben@unkin.net>
Reviewed-on: #47

internal/virtual/helm_merger.go

@@ -0,0 +1,92 @@
+package virtual
+
+import (
+	"fmt"
+	"strings"
+
+	"gopkg.in/yaml.v3"
+
+	"git.unkin.net/unkin/artifactapi/pkg/models"
+)
+
+func init() {
+	RegisterMerger(models.PackageHelm, &HelmMerger{})
+}
+
+type HelmMerger struct{}
+
+type helmIndex struct {
+	APIVersion string                        `yaml:"apiVersion"`
+	Entries    map[string][]helmChartVersion `yaml:"entries"`
+	Generated  string                        `yaml:"generated,omitempty"`
+}
+
+type helmChartVersion struct {
+	Name    string   `yaml:"name"`
+	Version string   `yaml:"version"`
+	URLs    []string `yaml:"urls"`
+	rest    map[string]any
+}
+
+func (m *HelmMerger) MergeIndexes(members []MemberIndex, proxyBaseURL string) ([]byte, error) {
+	merged := &helmIndex{
+		APIVersion: "v1",
+		Entries:    make(map[string][]helmChartVersion),
+	}
+
+	seen := map[string]map[string]bool{}
+
+	for _, member := range members {
+		var idx helmIndex
+		if err := yaml.Unmarshal(member.Body, &idx); err != nil {
+			continue
+		}
+
+		for chart, versions := range idx.Entries {
+			if seen[chart] == nil {
+				seen[chart] = map[string]bool{}
+			}
+			for _, ver := range versions {
+				key := chart + ":" + ver.Version
+				if seen[chart][ver.Version] {
+					continue
+				}
+				seen[chart][ver.Version] = true
+
+				if proxyBaseURL != "" {
+					for i, u := range ver.URLs {
+						if strings.HasPrefix(u, "http://") || strings.HasPrefix(u, "https://") {
+							ver.URLs[i] = fmt.Sprintf("%s/api/v1/remote/%s/%s",
+								strings.TrimRight(proxyBaseURL, "/"),
+								member.RemoteName,
+								extractPath(u))
+						} else {
+							ver.URLs[i] = fmt.Sprintf("%s/api/v1/remote/%s/%s",
+								strings.TrimRight(proxyBaseURL, "/"),
+								member.RemoteName,
+								u)
+						}
+					}
+				}
+
+				merged.Entries[chart] = append(merged.Entries[chart], ver)
+				_ = key
+			}
+		}
+	}
+
+	return yaml.Marshal(merged)
+}
+
+func extractPath(rawURL string) string {
+	idx := strings.Index(rawURL, "://")
+	if idx == -1 {
+		return rawURL
+	}
+	rest := rawURL[idx+3:]
+	slashIdx := strings.Index(rest, "/")
+	if slashIdx == -1 {
+		return ""
+	}
+	return rest[slashIdx+1:]
+}