Enhance CPU/GPU display for Apple Silicon

- Show all CPU cores instead of top 3 busiest
- Add P-CPU/E-CPU core grouping (Performance/Efficiency)
- Display GPU core count from system_profiler
- Add GPU usage meter via powermetrics (requires sudo)
- Show hint to run with sudo for GPU metrics

Tested on M2 Pro (6P + 4E cores, 16 GPU cores)

cmd/status/metrics_gpu.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"encoding/json"
 	"errors"
+	"regexp"
 	"runtime"
 	"strconv"
 	"strings"
@@ -13,17 +14,29 @@ import (
 const (
 	systemProfilerTimeout = 4 * time.Second
 	macGPUInfoTTL         = 10 * time.Minute
+	powermetricsTimeout   = 2 * time.Second
 )
 
 func (c *Collector) collectGPU(now time.Time) ([]GPUStatus, error) {
 	if runtime.GOOS == "darwin" {
-		if len(c.cachedGPU) > 0 && !c.lastGPUAt.IsZero() && now.Sub(c.lastGPUAt) < macGPUInfoTTL {
-			return c.cachedGPU, nil
+		// Get static GPU info (cached for 10 min)
+		if len(c.cachedGPU) == 0 || c.lastGPUAt.IsZero() || now.Sub(c.lastGPUAt) >= macGPUInfoTTL {
+			if gpus, err := readMacGPUInfo(); err == nil && len(gpus) > 0 {
+				c.cachedGPU = gpus
+				c.lastGPUAt = now
+			}
 		}
-		if gpus, err := readMacGPUInfo(); err == nil && len(gpus) > 0 {
-			c.cachedGPU = gpus
-			c.lastGPUAt = now
-			return gpus, nil
+
+		// Get real-time GPU usage
+		if len(c.cachedGPU) > 0 {
+			usage := getMacGPUUsage()
+			result := make([]GPUStatus, len(c.cachedGPU))
+			copy(result, c.cachedGPU)
+			// Apply usage to first GPU (Apple Silicon has one integrated GPU)
+			if len(result) > 0 {
+				result[0].Usage = usage
+			}
+			return result, nil
 		}
 	}
 
@@ -91,6 +104,7 @@ func readMacGPUInfo() ([]GPUStatus, error) {
 			VRAM   string `json:"spdisplays_vram"`
 			Vendor string `json:"spdisplays_vendor"`
 			Metal  string `json:"spdisplays_metal"`
+			Cores  string `json:"sppci_cores"`
 		} `json:"SPDisplaysDataType"`
 	}
 	if err := json.Unmarshal([]byte(out), &data); err != nil {
@@ -113,10 +127,12 @@ func readMacGPUInfo() ([]GPUStatus, error) {
 			noteParts = append(noteParts, d.Vendor)
 		}
 		note := strings.Join(noteParts, " · ")
+		coreCount, _ := strconv.Atoi(d.Cores)
 		gpus = append(gpus, GPUStatus{
-			Name:  d.Name,
-			Usage: -1,
-			Note:  note,
+			Name:      d.Name,
+			Usage:     -1, // Will be updated with real-time data
+			CoreCount: coreCount,
+			Note:      note,
 		})
 	}
 
@@ -129,3 +145,38 @@ func readMacGPUInfo() ([]GPUStatus, error) {
 
 	return gpus, nil
 }
+
+// getMacGPUUsage gets GPU active residency from powermetrics.
+// Returns -1 if unavailable (e.g., not running as root).
+func getMacGPUUsage() float64 {
+	ctx, cancel := context.WithTimeout(context.Background(), powermetricsTimeout)
+	defer cancel()
+
+	// powermetrics requires root, but we try anyway - some systems may have it enabled
+	out, err := runCmd(ctx, "powermetrics", "--samplers", "gpu_power", "-i", "500", "-n", "1")
+	if err != nil {
+		return -1
+	}
+
+	// Parse "GPU HW active residency:   X.XX%"
+	re := regexp.MustCompile(`GPU HW active residency:\s+([\d.]+)%`)
+	matches := re.FindStringSubmatch(out)
+	if len(matches) >= 2 {
+		usage, err := strconv.ParseFloat(matches[1], 64)
+		if err == nil {
+			return usage
+		}
+	}
+
+	// Fallback: parse "GPU idle residency: X.XX%" and calculate active
+	reIdle := regexp.MustCompile(`GPU idle residency:\s+([\d.]+)%`)
+	matchesIdle := reIdle.FindStringSubmatch(out)
+	if len(matchesIdle) >= 2 {
+		idle, err := strconv.ParseFloat(matchesIdle[1], 64)
+		if err == nil {
+			return 100.0 - idle
+		}
+	}
+
+	return -1
+}