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/src/wled_controller/api/routes/system.py

@@ -1,8 +1,9 @@
-"""System routes: health, version, displays."""
+"""System routes: health, version, displays, performance."""
 
 import sys
 from datetime import datetime
 
+import psutil
 from fastapi import APIRouter, HTTPException
 
 from wled_controller import __version__
@@ -10,7 +11,9 @@ from wled_controller.api.auth import AuthRequired
 from wled_controller.api.schemas.system import (
     DisplayInfo,
     DisplayListResponse,
+    GpuInfo,
     HealthResponse,
+    PerformanceResponse,
     ProcessListResponse,
     VersionResponse,
 )
@@ -19,6 +22,23 @@ from wled_controller.utils import get_logger
 
 logger = get_logger(__name__)
 
+# Prime psutil CPU counter (first call always returns 0.0)
+psutil.cpu_percent(interval=None)
+
+# Try to initialize NVIDIA GPU monitoring
+_nvml_available = False
+try:
+    import pynvml as _pynvml_mod  # nvidia-ml-py (the pynvml wrapper is deprecated)
+
+    _pynvml_mod.nvmlInit()
+    _nvml_handle = _pynvml_mod.nvmlDeviceGetHandleByIndex(0)
+    _nvml_available = True
+    _nvml = _pynvml_mod
+    logger.info(f"NVIDIA GPU monitoring enabled: {_nvml.nvmlDeviceGetName(_nvml_handle)}")
+except Exception:
+    _nvml = None
+    logger.info("NVIDIA GPU monitoring unavailable (pynvml not installed or no NVIDIA GPU)")
+
 router = APIRouter()
 
 
@@ -113,3 +133,40 @@ async def get_running_processes(_: AuthRequired):
             status_code=500,
             detail=f"Failed to retrieve process list: {str(e)}"
         )
+
+
+@router.get(
+    "/api/v1/system/performance",
+    response_model=PerformanceResponse,
+    tags=["Config"],
+)
+async def get_system_performance(_: AuthRequired):
+    """Get current system performance metrics (CPU, RAM, GPU)."""
+    mem = psutil.virtual_memory()
+
+    gpu = None
+    if _nvml_available:
+        try:
+            util = _nvml.nvmlDeviceGetUtilizationRates(_nvml_handle)
+            mem_info = _nvml.nvmlDeviceGetMemoryInfo(_nvml_handle)
+            temp = _nvml.nvmlDeviceGetTemperature(
+                _nvml_handle, _nvml.NVML_TEMPERATURE_GPU
+            )
+            gpu = GpuInfo(
+                name=_nvml.nvmlDeviceGetName(_nvml_handle),
+                utilization=float(util.gpu),
+                memory_used_mb=round(mem_info.used / 1024 / 1024, 1),
+                memory_total_mb=round(mem_info.total / 1024 / 1024, 1),
+                temperature_c=float(temp),
+            )
+        except Exception:
+            pass
+
+    return PerformanceResponse(
+        cpu_percent=psutil.cpu_percent(interval=None),
+        ram_used_mb=round(mem.used / 1024 / 1024, 1),
+        ram_total_mb=round(mem.total / 1024 / 1024, 1),
+        ram_percent=mem.percent,
+        gpu=gpu,
+        timestamp=datetime.utcnow(),
+    )