Monitor: show GPU temperature and fan speed

Extends the existing per-tick nvidia-smi query with temperature.gpu and
fan.speed (no extra call); N/A values (cards without fan telemetry) are
simply omitted from the GPU line.

internal/game/game.go

@@ -186,27 +186,54 @@ func queryComputeApps(ctx context.Context) ([]computeApp, error) {
 	return parseComputeApps(string(out))
 }
 
-// QueryVRAMMB returns used and total GPU VRAM in MiB via nvidia-smi.
-// Unlike the per-process list this works under WDDM too.
-func QueryVRAMMB(ctx context.Context) (used, total int, err error) {
+// GPUStats is one nvidia-smi reading of the whole card.
+type GPUStats struct {
+	UsedMB  int
+	TotalMB int
+	TempC   int // -1 when nvidia-smi reports N/A
+	FanPct  int // -1 when N/A (some cards don't expose the fan)
+}
+
+// QueryGPUStats returns VRAM usage, temperature and fan speed via
+// nvidia-smi. Unlike the per-process list this works under WDDM too.
+func QueryGPUStats(ctx context.Context) (GPUStats, error) {
 	out, err := exec.CommandContext(ctx, "nvidia-smi",
-		"--query-gpu=memory.used,memory.total", "--format=csv,noheader,nounits").Output()
+		"--query-gpu=memory.used,memory.total,temperature.gpu,fan.speed", "--format=csv,noheader,nounits").Output()
 	if err != nil {
-		return 0, 0, err
+		return GPUStats{}, err
 	}
-	usedStr, totalStr, ok := strings.Cut(strings.TrimSpace(string(out)), ",")
-	if !ok {
-		return 0, 0, fmt.Errorf("nvidia-smi: unexpected output %q", strings.TrimSpace(string(out)))
+	return parseGPUStats(string(out))
+}
+
+// parseGPUStats parses one "used, total, temp, fan" CSV line (MiB, °C,
+// percent). The memory fields must be numeric; temperature and fan fall
+// back to -1 on "N/A" and friends.
+func parseGPUStats(out string) (GPUStats, error) {
+	fields := strings.Split(strings.TrimSpace(out), ",")
+	if len(fields) != 4 {
+		return GPUStats{}, fmt.Errorf("nvidia-smi: unexpected output %q", strings.TrimSpace(out))
 	}
-	used, err = strconv.Atoi(strings.TrimSpace(usedStr))
-	if err != nil {
-		return 0, 0, fmt.Errorf("nvidia-smi: unexpected used memory in %q", strings.TrimSpace(string(out)))
+	num := func(s string) (int, error) {
+		return strconv.Atoi(strings.TrimSpace(s))
 	}
-	total, err = strconv.Atoi(strings.TrimSpace(totalStr))
-	if err != nil {
-		return 0, 0, fmt.Errorf("nvidia-smi: unexpected total memory in %q", strings.TrimSpace(string(out)))
+	optional := func(s string) int {
+		n, err := num(s)
+		if err != nil {
+			return -1
+		}
+		return n
 	}
-	return used, total, nil
+	var st GPUStats
+	var err error
+	if st.UsedMB, err = num(fields[0]); err != nil {
+		return GPUStats{}, fmt.Errorf("nvidia-smi: unexpected used memory in %q", strings.TrimSpace(out))
+	}
+	if st.TotalMB, err = num(fields[1]); err != nil {
+		return GPUStats{}, fmt.Errorf("nvidia-smi: unexpected total memory in %q", strings.TrimSpace(out))
+	}
+	st.TempC = optional(fields[2])
+	st.FanPct = optional(fields[3])
+	return st, nil
 }
 
 // parseComputeApps parses "pid, used_memory" CSV lines (no header, MiB