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/Dockerfile

@@ -0,0 +1,45 @@
+# Build stage
+FROM golang:1.21-alpine AS builder
+
+WORKDIR /app
+
+# Install dependencies
+RUN apk add --no-cache git
+
+# Copy go mod files
+COPY go.mod go.sum* ./
+RUN go mod download
+
+# Copy source code
+COPY . .
+
+# Build binary
+RUN CGO_ENABLED=0 GOOS=linux go build -ldflags="-s -w" -o /server ./cmd/server
+
+# Final stage - minimal image
+FROM alpine:3.19
+
+RUN apk add --no-cache ca-certificates tzdata
+
+WORKDIR /app
+
+# Copy binary from builder
+COPY --from=builder /server /app/server
+
+# Create data directory
+RUN mkdir -p /data
+
+# Expose port
+EXPOSE 8080
+
+# Run as non-root user
+RUN adduser -D -u 1000 appuser
+RUN chown -R appuser:appuser /app /data
+USER appuser
+
+# Health check
+HEALTHCHECK --interval=30s --timeout=3s --start-period=5s --retries=3 \
+    CMD wget --no-verbose --tries=1 --spider http://localhost:8080/api/health || exit 1
+
+ENTRYPOINT ["/app/server"]
+CMD ["--port", "8080", "--data", "/data"]