Add real-time system performance charts to dashboard

Backend: GET /api/v1/system/performance endpoint using psutil (CPU/RAM)
and nvidia-ml-py (GPU utilization, memory, temperature) with graceful
fallback. Frontend: Chart.js line charts with rolling 60-sample history
persisted to sessionStorage, flicker-free updates via persistent DOM
and diff-based dynamic section refresh.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/pyproject.toml

@@ -39,6 +39,8 @@ dependencies = [
     "wmi>=1.5.1; sys_platform == 'win32'",
     "zeroconf>=0.131.0",
     "pyserial>=3.5",
+    "psutil>=5.9.0",
+    "nvidia-ml-py>=12.0.0; sys_platform == 'win32'",
 ]
 
 [project.optional-dependencies]