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

ui/src/pages/Dashboard.css

@@ -0,0 +1,47 @@
+.stats-row {
+  display: flex;
+  gap: 16px;
+  margin-bottom: 24px;
+  flex-wrap: wrap;
+}
+
+.health-row {
+  display: flex;
+  align-items: center;
+  gap: 10px;
+  margin-bottom: 28px;
+  padding: 12px 16px;
+  background: var(--bg-surface);
+  border: 1px solid var(--border);
+  border-radius: var(--radius);
+}
+
+.health-label {
+  font-size: 0.85em;
+  font-weight: 600;
+  color: var(--text-muted);
+  margin-right: 4px;
+}
+
+.section-title {
+  font-size: 1.1em;
+  font-weight: 600;
+  color: var(--text-bright);
+  margin-bottom: 12px;
+  margin-top: 8px;
+}
+
+.error-banner {
+  background: rgba(239, 68, 68, 0.1);
+  border: 1px solid var(--red);
+  color: var(--red);
+  padding: 12px 16px;
+  border-radius: var(--radius);
+  font-size: 0.9em;
+}
+
+.loading {
+  color: var(--text-muted);
+  font-size: 0.9em;
+  padding: 32px 0;
+}