feat(nodes): live CPU/RAM/disk monitoring in the node list

- node-agent: internal/metrics — read CPU% (GetSystemTimes), RAM (GlobalMemoryStatusEx),
  disk used%/total (GetDiskFreeSpaceEx) via stdlib kernel32 (no external dep; windows
  build + non-windows stub). Heartbeat now reports cpu_pct/ram_available_mb/disk_used_pct/
  disk_total_gb + ae_running.
- render-svc: heartbeat persists last_disk_pct + disk_total_gb (migration 29); RenderNode
  model + node SELECT/scan carry them.
- admin: rewrite NodesTable to the real RenderNode shape (fixes a pre-existing items/V2Node
  mismatch that left the list empty) + a CPU/RAM/disk bars column + stale-heartbeat flag.
- assets-bundle ingestion: ProjectMediaBundle (jszip) auto-maps project.zip → project/scene
  image/demo/colour + music; PatchProject gains image/full_demo/shared_colors_svg.
- scan: RGBA (4-number) colours recognised + frshare single-int controls detected.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

services/node-agent/internal/client/client.go

@@ -122,6 +122,8 @@ type HeartbeatRequest struct {
 	Status         string  `json:"status"` // Ready | Busy
 	CPUPct         *int    `json:"cpu_pct,omitempty"`
 	RAMAvailableMB *int    `json:"ram_available_mb,omitempty"`
+	DiskUsedPct    *int    `json:"disk_used_pct,omitempty"`
+	DiskTotalGB    *int    `json:"disk_total_gb,omitempty"`
 	AERunning      *bool   `json:"ae_running,omitempty"`
 	CurrentJobID   *string `json:"current_job_id,omitempty"`
 	CacheUsedGB    *int    `json:"cache_used_gb,omitempty"`