Add live transmitter position (status) alongside logged points

devices/<serial>/log messages now carry a "type": "log" or "status".
"log" persists a LocatePoint as before; "status" carries the same
position + telemetry shape but is broadcast live over the job's
realtime channel without touching locate_points — it's a current-
position update, not a recorded point.

The job map renders the latest status as a blue "you are here" marker
(with a soft accuracy-radius halo) that moves in place as new updates
arrive, separate from the colored polyline of logged points. Clicking
it shows the same detail readout as a logged point.

The simulator gained a message-type toggle (Log point / Status
update) so both paths can be exercised from /sim.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

backend/src/ingest/dto/mqtt-messages.dto.ts

@@ -6,6 +6,7 @@ import {
   IsArray,
   IsDateString,
   IsEnum,
+  IsIn,
   IsInt,
   IsNotEmpty,
   IsNumber,
@@ -139,10 +140,18 @@ export class MqttPointsMessageDto {
   points: MqttPointDto[];
 }
 
-// Single-reading log entry for a locator that publishes directly (or is
-// relayed) to devices/<serial>/log — the serial comes from the topic itself,
-// so identity is job-anchored rather than publisher-credential-anchored.
+export const MQTT_LOG_MESSAGE_TYPES = ['log', 'status'] as const;
+export type MqttLogMessageType = (typeof MQTT_LOG_MESSAGE_TYPES)[number];
+
+// Single reading for a locator that publishes directly (or is relayed) to
+// devices/<serial>/log — the serial comes from the topic itself, so identity
+// is job-anchored rather than publisher-credential-anchored. `type` decides
+// what happens to it: "log" persists a LocatePoint; "status" is an ephemeral
+// current-position update, broadcast live but never written to the DB.
 export class MqttLogMessageDto extends MqttPointDto {
+  @IsIn(MQTT_LOG_MESSAGE_TYPES)
+  type: MqttLogMessageType;
+
   @IsString()
   @IsNotEmpty()
   jobId: string;