Add harness app: agent orchestrator with cluster deployment

- Next.js app for orchestrating coding agent benchmarks (Claude Code, Codex, OpenCode)
- Dockerfile installs git, gh CLI, and agent CLIs for headless execution
- K8s deployment with workspace volume, sealed credentials for Claude + OpenCode
- Traefik IngressRoute at harness.coreworlds.io with internal-only middleware + TLS
- CI pipeline path filter for harness builds
- Fix OpenCode runtime flags (subcommand-based headless mode)

apps/harness/src/app/api/health/route.ts

@@ -0,0 +1,9 @@
+import { NextResponse } from "next/server";
+
+export async function GET() {
+  return NextResponse.json({
+    status: "ok",
+    service: "harness",
+    timestamp: new Date().toISOString(),
+  });
+}