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/proxy/circuit.go

@@ -0,0 +1,60 @@
+package proxy
+
+import (
+	"context"
+	"time"
+
+	"git.unkin.net/unkin/artifactapi/internal/cache"
+	"git.unkin.net/unkin/artifactapi/pkg/models"
+)
+
+const (
+	defaultCircuitThreshold = 5
+	defaultCircuitCooldown  = 60 * time.Second
+)
+
+type CircuitBreaker struct {
+	cache     *cache.Redis
+	threshold int64
+	cooldown  time.Duration
+}
+
+func NewCircuitBreaker(c *cache.Redis) *CircuitBreaker {
+	return &CircuitBreaker{
+		cache:     c,
+		threshold: defaultCircuitThreshold,
+		cooldown:  defaultCircuitCooldown,
+	}
+}
+
+func (cb *CircuitBreaker) IsOpen(ctx context.Context, remote string) bool {
+	failures, err := cb.cache.GetCircuitFailures(ctx, remote)
+	if err != nil {
+		return false
+	}
+	return failures >= cb.threshold
+}
+
+func (cb *CircuitBreaker) RecordFailure(ctx context.Context, remote string) {
+	cb.cache.IncrCircuitFailure(ctx, remote, cb.cooldown)
+}
+
+func (cb *CircuitBreaker) RecordSuccess(ctx context.Context, remote string) {
+	cb.cache.ResetCircuit(ctx, remote)
+}
+
+func (cb *CircuitBreaker) Health(ctx context.Context, remote string) models.RemoteHealth {
+	failures, err := cb.cache.GetCircuitFailures(ctx, remote)
+	if err != nil {
+		return models.RemoteHealth{Status: "unknown"}
+	}
+
+	switch {
+	case failures == 0:
+		return models.RemoteHealth{Status: "healthy", ConsecutiveFailures: int(failures)}
+	case failures < cb.threshold:
+		return models.RemoteHealth{Status: "degraded", ConsecutiveFailures: int(failures)}
+	default:
+		return models.RemoteHealth{Status: "down", ConsecutiveFailures: int(failures)}
+	}
+}