fix: serial decode offset, PPV label scan, debug mode for waveform records

- _decode_serial_number: read from data[11:] not data[:8] — was returning
  the LENGTH_ECHO byte (0x0A = '\n') instead of the serial string
- _extract_peak_floats: search for channel label strings ("Tran" etc) and
  read float at label+6; old step-4 aligned scan was reading trigger levels
  instead of PPV values
- get_events: add debug=False param; stashes raw 210-byte record on
  Event._raw_record when True for field-layout inspection
- server /device/events: add ?debug=true query param; includes
  raw_record_hex + raw_record_len in response when set
- models: add Event._raw_record optional bytes field

sfm/server.py

@@ -126,8 +126,8 @@ def _serialise_device_info(info: DeviceInfo) -> dict:
     }
 
 
-def _serialise_event(ev: Event) -> dict:
-    return {
+def _serialise_event(ev: Event, debug: bool = False) -> dict:
+    d: dict = {
         "index":        ev.index,
         "timestamp":    _serialise_timestamp(ev.timestamp),
         "sample_rate":  ev.sample_rate,
@@ -135,6 +135,11 @@ def _serialise_event(ev: Event) -> dict:
         "peak_values":  _serialise_peak_values(ev.peak_values),
         "project_info": _serialise_project_info(ev.project_info),
     }
+    if debug:
+        raw = getattr(ev, "_raw_record", None)
+        d["raw_record_hex"] = raw.hex() if raw else None
+        d["raw_record_len"] = len(raw) if raw else 0
+    return d
 
 
 # ── Transport factory ─────────────────────────────────────────────────────────
@@ -257,6 +262,7 @@ def device_events(
     baud:     int           = Query(38400,          description="Serial baud rate"),
     host:     Optional[str] = Query(None,          description="TCP host — modem IP or ACH relay"),
     tcp_port: int           = Query(DEFAULT_TCP_PORT, description=f"TCP port (default {DEFAULT_TCP_PORT})"),
+    debug:    bool          = Query(False,          description="Include raw record hex for field-layout inspection"),
 ) -> dict:
     """
     Connect to the device, read the event index, and download all stored
@@ -264,15 +270,18 @@ def device_events(
 
     Supply either *port* (serial) or *host* (TCP/modem).
 
+    Pass debug=true to include raw_record_hex in each event — useful for
+    verifying field offsets against the protocol reference.
+
     This does NOT download raw ADC waveform samples — those are large and
     fetched separately via GET /device/event/{idx}/waveform (future endpoint).
     """
-    log.info("GET /device/events  port=%s host=%s", port, host)
+    log.info("GET /device/events  port=%s host=%s debug=%s", port, host, debug)
 
     try:
         def _do():
             with _build_client(port, baud, host, tcp_port) as client:
-                return client.connect(), client.get_events()
+                return client.connect(), client.get_events(debug=debug)
         info, events = _run_with_retry(_do, is_tcp=_is_tcp(host))
     except HTTPException:
         raise
@@ -286,7 +295,7 @@ def device_events(
     return {
         "device":      _serialise_device_info(info),
         "event_count": len(events),
-        "events":      [_serialise_event(ev) for ev in events],
+        "events":      [_serialise_event(ev, debug=debug) for ev in events],
     }