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/config/env.go

@@ -0,0 +1,72 @@
+package config
+
+import (
+	"fmt"
+	"os"
+	"strconv"
+)
+
+type Config struct {
+	ListenAddr string
+
+	DBHost string
+	DBPort int
+	DBUser string
+	DBPass string
+	DBName string
+	DBSSL  string
+
+	RedisURL string
+
+	S3Endpoint  string
+	S3AccessKey string
+	S3SecretKey string
+	S3Bucket    string
+	S3Secure    bool
+	S3Region    string
+}
+
+func (c *Config) DatabaseDSN() string {
+	return fmt.Sprintf(
+		"postgres://%s:%s@%s:%d/%s?sslmode=%s",
+		c.DBUser, c.DBPass, c.DBHost, c.DBPort, c.DBName, c.DBSSL,
+	)
+}
+
+func Load() (*Config, error) {
+	dbPort, err := strconv.Atoi(getenv("DBPORT", "5432"))
+	if err != nil {
+		return nil, fmt.Errorf("invalid DBPORT: %w", err)
+	}
+
+	s3Secure, _ := strconv.ParseBool(getenv("MINIO_SECURE", "false"))
+
+	cfg := &Config{
+		ListenAddr: getenv("LISTEN_ADDR", ":8000"),
+
+		DBHost: getenv("DBHOST", "localhost"),
+		DBPort: dbPort,
+		DBUser: getenv("DBUSER", "artifacts"),
+		DBPass: getenv("DBPASS", ""),
+		DBName: getenv("DBNAME", "artifacts"),
+		DBSSL:  getenv("DBSSL", "disable"),
+
+		RedisURL: getenv("REDIS_URL", "redis://localhost:6379"),
+
+		S3Endpoint:  getenv("MINIO_ENDPOINT", "localhost:9000"),
+		S3AccessKey: getenv("MINIO_ACCESS_KEY", ""),
+		S3SecretKey: getenv("MINIO_SECRET_KEY", ""),
+		S3Bucket:    getenv("MINIO_BUCKET", "artifacts"),
+		S3Secure:    s3Secure,
+		S3Region:    getenv("MINIO_REGION", ""),
+	}
+
+	return cfg, nil
+}
+
+func getenv(key, fallback string) string {
+	if v := os.Getenv(key); v != "" {
+		return v
+	}
+	return fallback
+}