Add HIOKI channel range controls and live range display

- GUI: voltage/current range selectors for Ch5 and Ch6 with AUTO option
- Worker: queries current V/I ranges each poll cycle, pushes to GUI
- Setting a fixed range automatically disables auto-range for that channel
- Live display shows current range values below each channel's readout

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

testbench/gui_workers.py

@@ -39,6 +39,10 @@ class Cmd(Enum):
     SET_COUPLING = auto()
     SET_RESPONSE_SPEED = auto()
     SET_AVERAGING = auto()
+    SET_VOLTAGE_RANGE = auto()
+    SET_CURRENT_RANGE = auto()
+    SET_VOLTAGE_AUTO = auto()
+    SET_CURRENT_AUTO = auto()
 
     # System
     SET_INTERVAL = auto()
@@ -108,6 +112,16 @@ class InstrumentWorker(threading.Thread):
                     data["load_on"] = self.bench.load.get_load_state()
                 except Exception:
                     data["load_on"] = None
+                # Query meter channel ranges
+                for ch in (5, 6):
+                    try:
+                        data[f"v_range_{ch}"] = self.bench.meter.get_voltage_range(ch).strip()
+                    except Exception:
+                        data[f"v_range_{ch}"] = None
+                    try:
+                        data[f"i_range_{ch}"] = self.bench.meter.get_current_range(ch).strip()
+                    except Exception:
+                        data[f"i_range_{ch}"] = None
             except Exception as e:
                 data = {"_error": str(e), "_timestamp": time.time()}
 
@@ -181,6 +195,16 @@ class InstrumentWorker(threading.Thread):
                     bench.meter.set_response_speed(args[0])
                 case Cmd.SET_AVERAGING:
                     bench.meter.set_averaging(args[0], args[1] if len(args) > 1 else None)
+                case Cmd.SET_VOLTAGE_RANGE:
+                    bench.meter.set_voltage_auto(args[0], False)
+                    bench.meter.set_voltage_range(args[0], args[1])
+                case Cmd.SET_CURRENT_RANGE:
+                    bench.meter.set_current_auto(args[0], False)
+                    bench.meter.set_current_range(args[0], args[1])
+                case Cmd.SET_VOLTAGE_AUTO:
+                    bench.meter.set_voltage_auto(args[0], args[1])
+                case Cmd.SET_CURRENT_AUTO:
+                    bench.meter.set_current_auto(args[0], args[1])
 
                 # System
                 case Cmd.SET_INTERVAL: