feat: v3 Go rewrite — full artifact proxy with web UI, TUI, and Terraform provider

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)

internal/provider/helm/helm.go

@@ -0,0 +1,58 @@
+package helm
+
+import (
+	"context"
+	"net/http"
+	"strings"
+
+	"git.unkin.net/unkin/artifactapi/internal/auth"
+	"git.unkin.net/unkin/artifactapi/internal/provider"
+	"git.unkin.net/unkin/artifactapi/pkg/models"
+)
+
+func init() {
+	provider.Register(&Provider{})
+}
+
+type Provider struct{}
+
+func (p *Provider) Type() models.PackageType { return models.PackageHelm }
+
+func (p *Provider) Classify(path string) provider.Mutability {
+	if strings.HasSuffix(path, "index.yaml") || strings.HasSuffix(path, "index.yml") {
+		return provider.Mutable
+	}
+	return provider.Immutable
+}
+
+func (p *Provider) ContentType(path string) string {
+	if strings.HasSuffix(path, ".tgz") || strings.HasSuffix(path, ".tar.gz") {
+		return "application/gzip"
+	}
+	if strings.HasSuffix(path, ".yaml") || strings.HasSuffix(path, ".yml") {
+		return "text/yaml"
+	}
+	return "application/octet-stream"
+}
+
+func (p *Provider) UpstreamURL(remote models.Remote, path string) string {
+	return strings.TrimRight(remote.BaseURL, "/") + "/" + strings.TrimLeft(path, "/")
+}
+
+func (p *Provider) RewriteResponse(body []byte, remote models.Remote, proxyBaseURL string) ([]byte, error) {
+	if proxyBaseURL == "" {
+		return nil, nil
+	}
+	content := string(body)
+	baseURL := strings.TrimRight(remote.BaseURL, "/")
+	proxyURL := strings.TrimRight(proxyBaseURL, "/") + "/api/v1/remote/" + remote.Name
+	rewritten := strings.ReplaceAll(content, baseURL, proxyURL)
+	if rewritten == content {
+		return nil, nil
+	}
+	return []byte(rewritten), nil
+}
+
+func (p *Provider) AuthHeaders(_ context.Context, remote models.Remote) (http.Header, error) {
+	return auth.BasicHeaders(remote), nil
+}

internal/provider/helm/helm_test.go

@@ -0,0 +1,51 @@
+package helm_test
+
+import (
+	"strings"
+	"testing"
+
+	"git.unkin.net/unkin/artifactapi/internal/provider"
+	"git.unkin.net/unkin/artifactapi/internal/provider/helm"
+	"git.unkin.net/unkin/artifactapi/pkg/models"
+)
+
+func TestProvider_Type(t *testing.T) {
+	p := &helm.Provider{}
+	if p.Type() != models.PackageHelm {
+		t.Errorf("expected helm, got %q", p.Type())
+	}
+}
+
+func TestProvider_Classify(t *testing.T) {
+	p := &helm.Provider{}
+	tests := []struct {
+		path string
+		want provider.Mutability
+	}{
+		{"index.yaml", provider.Mutable},
+		{"index.yml", provider.Mutable},
+		{"chart-1.0.tgz", provider.Immutable},
+		{"charts/nginx-1.0.tgz", provider.Immutable},
+	}
+	for _, tt := range tests {
+		if got := p.Classify(tt.path); got != tt.want {
+			t.Errorf("Classify(%q) = %v, want %v", tt.path, got, tt.want)
+		}
+	}
+}
+
+func TestProvider_RewriteResponse(t *testing.T) {
+	p := &helm.Provider{}
+	body := []byte("urls:\n- https://charts.example.com/chart-1.0.tgz")
+	remote := models.Remote{Name: "helm-test", BaseURL: "https://charts.example.com"}
+	rewritten, err := p.RewriteResponse(body, remote, "https://proxy.example.com")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if rewritten == nil {
+		t.Fatal("expected rewrite")
+	}
+	if !strings.Contains(string(rewritten), "proxy.example.com/api/v1/remote/helm-test") {
+		t.Errorf("expected proxy URL in body: %s", rewritten)
+	}
+}