feat: Implement Phase 2 dashboard for K8s agent system

Lightweight Go-based dashboard for Raspberry Pi cluster:

Backend:
- chi router with REST API
- Embedded static file serving
- JSON file-based state storage
- Health checks and CORS support

Frontend:
- Responsive dark theme UI
- Status view with nodes, alerts, ArgoCD apps
- Pending actions with approve/reject
- Action history and audit trail
- Workflow listing and manual triggers

Deployment:
- Multi-stage Dockerfile (small Alpine image)
- Kubernetes manifests with Pi 3 tolerations
- Resource limits: 32-64Mi memory, 10-100m CPU
- ArgoCD application manifest
- Kustomize configuration

API endpoints:
- GET /api/status - Cluster status
- GET/POST /api/pending - Action management
- GET /api/history - Action audit trail
- GET/POST /api/workflows - Workflow management

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

dashboard/go.sum

@@ -0,0 +1,4 @@
+github.com/go-chi/chi/v5 v5.0.11 h1/BnpYbFZ3T3S1WMpD79r7R5ThWX40TaFB7L31Y8xqSwA=
+github.com/go-chi/chi/v5 v5.0.11/go.mod h1/DslCQbL2OYiznFReuXYUmQ2hGd1aDpCnlMNITLSKoi8=
+github.com/go-chi/cors v1.2.1 h1:xEC8UT3Rlp2QuWNEr4Fs/c2EAGVKBwy/1vHx3bppil4=
+github.com/go-chi/cors v1.2.1/go.mod h1:sSbTewc+6wYHBBCW7ytsFSn3rn0gOeEOrPIsEDqiK+0=