feat(audit): fan-stress SAT for MSI case-04 fan lag & thermal throttle detection

Two-phase GPU thermal cycling test with per-second telemetry:
- Phases: baseline → load1 → pause (no cooldown) → load2 → cooldown
- Monitors: fan RPM (ipmitool sdr), CPU/server temps (ipmitool/sensors),
  system power (ipmitool dcmi), GPU temp/power/usage/clock/throttle (nvidia-smi)
- Detects throttling via clocks_throttle_reasons.active bitmask
- Measures fan response lag from load start (validates case-04 ~2s lag)
- Exports metrics.csv (wide format, one row/sec) and fan-sensors.csv (long format)
- TUI: adds [F] Fan Stress Test to Health Check screen with Quick/Standard/Express modes

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

audit/internal/app/app_test.go

@@ -170,6 +170,10 @@ func (f fakeSAT) RunAMDAcceptancePack(baseDir string) (string, error) {
 	return "", nil
 }
 
+func (f fakeSAT) RunFanStressTest(_ context.Context, _ string, _ platform.FanStressOptions) (string, error) {
+	return "", nil
+}
+
 func TestNetworkStatusFormatsInterfacesAndRoute(t *testing.T) {
 	t.Parallel()