Add eBPF observability: GetSockmapStats, ListMeshRedirects, GetRateLimitStats

[piwi3910]

Summary

Several NovaNet eBPF observability APIs are not wrapped in the NovaEdge client and not exposed via metrics or admin API:

1. GetSockmapStats — SOCKMAP redirect/fallback counters (not wrapped in client.go)
2. ListMeshRedirects — active sk_lookup mesh redirect entries (not wrapped in client.go)
3. GetRateLimitStats — per-CIDR allowed/denied counters (wrapped but never called)
4. StreamBackendHealth — passive health data stream (not wrapped in client.go)

What's Needed

1. Add missing client wrappers for GetSockmapStats, ListMeshRedirects, StreamBackendHealth
2. Expose SOCKMAP stats as Prometheus metrics (novaedge_sockmap_redirected_total, novaedge_sockmap_fallback_total)
3. Expose mesh redirect count as gauge (novaedge_mesh_ebpf_redirects_active)
4. Expose rate limit stats as counters (novaedge_ratelimit_ebpf_allowed_total, novaedge_ratelimit_ebpf_denied_total)
5. Add novactl mesh status output showing eBPF acceleration state

Acceptance Criteria

• All NovaNet observability APIs wrapped in client
• Prometheus metrics for SOCKMAP, mesh redirect, rate limit eBPF stats
• Periodic polling goroutine to refresh eBPF stats
• Admin API endpoint for eBPF acceleration status