Tie points to locator serial numbers and store receiver telemetry

Adds devices/<serial>/log as a job-anchored MQTT ingest path: a locator
identifies itself by serial in the topic (auto-registered on first
sight, org resolved from the job in the payload) rather than by a
pre-provisioned broker credential. Device.serialNumber is now globally
unique so the bare topic segment is enough to resolve identity.
Locator lookup/auto-register logic is shared (LocatorRegistryService)
between this and the existing devices/<mqttUsername>/points path.

New /sim page (own header, outside the main app nav) simulates a
transmitter: pick an open job or create one, set a serial number and
telemetry defaults, and send points one at a time or on an interval
along a simulated walking path. It calls a new authenticated backend
endpoint (POST /orgs/:orgId/sim/publish) that publishes onto the real
broker rather than writing the DB directly, so the simulator exercises
the actual ingest pipeline end-to-end.

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

backend/prisma/migrations/20260714163000_global_serial_unique/migration.sql

@@ -0,0 +1,8 @@
+-- Locator serial numbers are globally unique (not per-org), so a bare
+-- devices/<serial>/log MQTT topic can identify the device without org context.
+
+-- DropIndex
+DROP INDEX "devices_orgId_serialNumber_key";
+
+-- CreateIndex
+CREATE UNIQUE INDEX "devices_serialNumber_key" ON "devices"("serialNumber");