feat(mqtt): add device health telemetry and migrate to v2 topic spec

Two efforts that landed together because the v2 topic work extends
tables the health-telemetry effort added days earlier in the same
files/functions, making them impractical to separate cleanly:

Health/diagnostics telemetry (schema, Jul 13-17):
- New Postgres tables: device_alert_events, device_boot_events,
  device_ping_samples, device_diagnostics_reports, plus a `source`
  column on device_logs to distinguish log origins
- Query/service layer in pg_mqtt.py and database/__init__.py for
  inserting and listing this history, plus a "latest metrics" endpoint
  combining most-recent diagnostics + ping RTT per device
- mqtt/router.py gains list endpoints for alert/boot/ping/diagnostics
  history, consumed by the upcoming Health tab

MQTT v2 topic migration (Sep 21):
- Heartbeat payload flattened per vesper_mqtt_topic_spec_v2.md, adding
  rssi/free_heap/state/ok fields
- Command replies move to control/ack, device-initiated events to
  control/reports; mqtt/client.py subscribes to the new topic set and
  runs a ping_loop (wired up in main.py) for RTT sampling
- mqtt/logger.py and pg_mqtt.py updated to parse and persist the new
  payload shape alongside the legacy fields for backwards compatibility

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

backend/database/__init__.py

@@ -16,6 +16,31 @@ from database.pg_mqtt import (
     upsert_alert,
     delete_alert,
     get_alerts,
+    insert_alert_event,
+    get_latest_alert_events,
+    get_latest_alert_event,
+    get_alert_events,
+    insert_boot_event,
+    get_boot_events,
+    get_latest_boot_event,
+    insert_ping_sample,
+    get_ping_samples,
+    get_latest_ping_samples,
+    insert_diagnostics_report,
+    get_diagnostics_reports,
+    get_latest_diagnostics_report,
+    get_latest_diagnostics_reports,
+    insert_report,
+    get_reports,
+    delete_device_logs,
+    delete_device_heartbeats,
+    delete_device_commands,
+    delete_device_alert_events,
+    delete_device_current_alerts,
+    delete_device_boot_events,
+    delete_device_ping_samples,
+    delete_device_diagnostics_reports,
+    delete_device_reports,
     partition_manager_loop,
     ensure_current_partitions,
 )
@@ -42,6 +67,31 @@ __all__ = [
     "upsert_alert",
     "delete_alert",
     "get_alerts",
+    "insert_alert_event",
+    "get_latest_alert_events",
+    "get_latest_alert_event",
+    "get_alert_events",
+    "insert_boot_event",
+    "get_boot_events",
+    "get_latest_boot_event",
+    "insert_ping_sample",
+    "get_ping_samples",
+    "get_latest_ping_samples",
+    "insert_diagnostics_report",
+    "get_diagnostics_reports",
+    "get_latest_diagnostics_report",
+    "get_latest_diagnostics_reports",
+    "insert_report",
+    "get_reports",
+    "delete_device_logs",
+    "delete_device_heartbeats",
+    "delete_device_commands",
+    "delete_device_alert_events",
+    "delete_device_current_alerts",
+    "delete_device_boot_events",
+    "delete_device_ping_samples",
+    "delete_device_diagnostics_reports",
+    "delete_device_reports",
     "partition_manager_loop",
     "ensure_current_partitions",
 ]