Report per-core CPU percentages alongside the overall figure

Derived from the same percpu psutil.cpu_percent() call rather than a
second blocking call, so the aggregate and the per-core breakdown
describe the same sampling window.

app/stats.py

@@ -183,7 +183,12 @@ def _network() -> dict:
 
 
 def collect() -> dict:
-    cpu_percent = psutil.cpu_percent(interval=0.3)
+    # A single percpu=True call gives every core's percent over the same
+    # sampling window; the overall figure is derived from it (its mean)
+    # instead of a second separate blocking call, so both numbers describe
+    # the same 0.3s window rather than two slightly different ones.
+    per_core_percent = psutil.cpu_percent(interval=0.3, percpu=True)
+    cpu_percent = round(sum(per_core_percent) / len(per_core_percent), 1) if per_core_percent else 0.0
     vm = psutil.virtual_memory()
     swap = psutil.swap_memory()
     boot_time = psutil.boot_time()
@@ -197,6 +202,7 @@ def collect() -> dict:
             "cores": psutil.cpu_count(logical=True) or 0,
             "model": _cpu_model(),
             "loadAverage": _load_average(),
+            "perCore": per_core_percent,
         },
         "memory": {
             "totalBytes": vm.total,