fix: v3 payload byte 1 layout — 10-bit sensor data, button on bit 2

Sens'it Discovery v3 byte 1 layout per official spec:
  bits 7-3: mode
  bit 2   : special / button alert
  bits 1-0: MSB (2 bits) of sensor data

Previous decoder had button on bit 0 and used only bit 2 as data MSB
(9-bit values). Real payloads confirmed 10-bit: e.g. b609a861 was
decoded as -4°C but correctly resolves to 28°C with the fixed layout.

Fixes applied consistently to all v3 modes:
- Temperature: 10-bit temp with formula (raw - 200) / 8
- Light: 10-bit brightness with formula raw / 96
- Door/Vibration/Magnet: 2-bit status from bits 1-0

Existing DB entries re-decoded in place.

dashboard/sensit_decoder.py

@@ -18,8 +18,13 @@ V3_MODES = {
 
 
 def _decode_v3(b0: int, b1: int, b2: int, b3: int) -> dict:
+    # byte 1 layout per Sens'it Discovery v3 spec:
+    #   bits 7-3: mode
+    #   bit 2   : special / button alert
+    #   bits 1-0: 2 MSB bits of sensor data (giving 10-bit values with b2)
     battery_raw = (b0 >> 3) & 0x1F
     mode = (b1 >> 3) & 0x1F
+    data_msb = b1 & 0x03
     result = {
         "format": "sensit_v3",
         "battery": round(battery_raw * 0.05 + 2.7, 2),
@@ -27,24 +32,24 @@ def _decode_v3(b0: int, b1: int, b2: int, b3: int) -> dict:
         "reserved_ok": True,
         "mode": V3_MODES.get(mode, f"Unknown ({mode})"),
         "mode_id": mode,
-        "button_alert": bool(b1 & 0x01),
+        "button_alert": bool((b1 >> 2) & 0x01),
     }
 
-    if mode == 1:  # Temperature + Humidity
-        temp_raw = (((b1 >> 2) & 0x01) << 8) | b2
+    if mode == 1:  # Temperature + Humidity (10-bit temp)
+        temp_raw = (data_msb << 8) | b2
         result["temperature_c"] = round((temp_raw - 200) / 8, 2)
         result["humidity_pct"] = round(b3 / 2, 1)
-    elif mode == 2:  # Light
-        brightness_raw = (((b1 >> 2) & 0x01) << 8) | b2
+    elif mode == 2:  # Light (10-bit brightness)
+        brightness_raw = (data_msb << 8) | b2
         result["brightness_lux"] = round(brightness_raw / 96, 2)
     elif mode == 3:
-        result["door_status"] = {0: "closed", 1: "opened", 2: "opening_alert", 3: "closing_alert"}.get((b1 >> 1) & 0x03, "unknown")
+        result["door_status"] = {0: "closed", 1: "opened", 2: "opening_alert", 3: "closing_alert"}.get(data_msb, "unknown")
         result["event_count"] = (b2 << 8) | b3
     elif mode == 4:
-        result["vibration_status"] = {0: "no_vibration", 1: "vibration_detected"}.get((b1 >> 1) & 0x03, "unknown")
+        result["vibration_status"] = {0: "no_vibration", 1: "vibration_detected"}.get(data_msb, "unknown")
         result["event_count"] = (b2 << 8) | b3
     elif mode == 5:
-        result["magnet_status"] = {0: "no_magnet", 1: "magnet_detected"}.get((b1 >> 1) & 0x03, "unknown")
+        result["magnet_status"] = {0: "no_magnet", 1: "magnet_detected"}.get(data_msb, "unknown")
         result["event_count"] = (b2 << 8) | b3
     return result