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_test.go

@@ -0,0 +1,124 @@
+package virtual_test
+
+import (
+	"strings"
+	"testing"
+
+	"git.unkin.net/unkin/artifactapi/internal/virtual"
+)
+
+func TestHelmMerger_BasicMerge(t *testing.T) {
+	m := &virtual.HelmMerger{}
+
+	member1 := virtual.MemberIndex{
+		RemoteName: "repo-a",
+		Body: []byte(`apiVersion: v1
+entries:
+  nginx:
+    - name: nginx
+      version: "1.0.0"
+      urls:
+        - https://charts-a.example.com/nginx-1.0.0.tgz
+`),
+	}
+
+	member2 := virtual.MemberIndex{
+		RemoteName: "repo-b",
+		Body: []byte(`apiVersion: v1
+entries:
+  redis:
+    - name: redis
+      version: "2.0.0"
+      urls:
+        - https://charts-b.example.com/redis-2.0.0.tgz
+`),
+	}
+
+	result, err := m.MergeIndexes([]virtual.MemberIndex{member1, member2}, "https://proxy.example.com")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	body := string(result)
+	if !strings.Contains(body, "nginx") {
+		t.Error("expected nginx in merged index")
+	}
+	if !strings.Contains(body, "redis") {
+		t.Error("expected redis in merged index")
+	}
+	if !strings.Contains(body, "proxy.example.com/api/v1/remote/repo-a") {
+		t.Error("expected proxy URL for repo-a")
+	}
+	if !strings.Contains(body, "proxy.example.com/api/v1/remote/repo-b") {
+		t.Error("expected proxy URL for repo-b")
+	}
+}
+
+func TestHelmMerger_Dedup(t *testing.T) {
+	m := &virtual.HelmMerger{}
+
+	idx := []byte(`apiVersion: v1
+entries:
+  nginx:
+    - name: nginx
+      version: "1.0.0"
+      urls:
+        - nginx-1.0.0.tgz
+`)
+
+	members := []virtual.MemberIndex{
+		{RemoteName: "repo-a", Body: idx},
+		{RemoteName: "repo-b", Body: idx},
+	}
+
+	result, err := m.MergeIndexes(members, "")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	count := strings.Count(string(result), "name: nginx")
+	if count != 1 {
+		t.Errorf("expected 1 entry for nginx, got %d\n%s", count, result)
+	}
+}
+
+func TestHelmMerger_PriorityOrder(t *testing.T) {
+	m := &virtual.HelmMerger{}
+
+	member1 := virtual.MemberIndex{
+		RemoteName: "priority-repo",
+		Body: []byte(`apiVersion: v1
+entries:
+  chart:
+    - name: chart
+      version: "1.0.0"
+      urls:
+        - chart-from-priority.tgz
+`),
+	}
+
+	member2 := virtual.MemberIndex{
+		RemoteName: "fallback-repo",
+		Body: []byte(`apiVersion: v1
+entries:
+  chart:
+    - name: chart
+      version: "1.0.0"
+      urls:
+        - chart-from-fallback.tgz
+`),
+	}
+
+	result, err := m.MergeIndexes([]virtual.MemberIndex{member1, member2}, "https://proxy")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	body := string(result)
+	if !strings.Contains(body, "priority-repo") {
+		t.Error("expected priority repo URL to win")
+	}
+	if strings.Contains(body, "fallback-repo") {
+		t.Error("expected fallback repo to be excluded for duplicate")
+	}
+}