Fix event loop blocking from perf endpoint and profile detection

- Change /api/v1/system/performance from async def to def so FastAPI
  runs the blocking psutil + NVML GPU queries in a thread pool instead
  of freezing the event loop (polled every 2s by dashboard)
- Batch profile engine's 3 separate run_in_executor detection calls
  into a single _detect_all_sync() call, reducing event loop wake-ups

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

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

@@ -140,8 +140,13 @@ async def get_running_processes(_: AuthRequired):
     response_model=PerformanceResponse,
     tags=["Config"],
 )
-async def get_system_performance(_: AuthRequired):
-    """Get current system performance metrics (CPU, RAM, GPU)."""
+def get_system_performance(_: AuthRequired):
+    """Get current system performance metrics (CPU, RAM, GPU).
+
+    Uses sync ``def`` so FastAPI runs it in a thread pool — the psutil
+    and NVML calls are blocking and would stall the event loop if run
+    in an ``async def`` handler.
+    """
     mem = psutil.virtual_memory()
 
     gpu = None