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/mqtt/models.py

@@ -27,6 +27,7 @@ class DeviceLogEntry(BaseModel):
     level: str
     message: str
     device_timestamp: Optional[int] = None
+    source: str = "log"
     received_at: str
 
 
@@ -39,6 +40,10 @@ class HeartbeatEntry(BaseModel):
     gateway: Optional[str] = None
     uptime_ms: Optional[int] = None
     uptime_display: Optional[str] = None
+    rssi: Optional[int] = None
+    free_heap: Optional[int] = None
+    state: Optional[str] = None  # "idle" | "playing" | "paused" | "error" | "booting" (v2 firmware only)
+    ok: Optional[bool] = None    # overall device health, independent of playback state (v2 firmware only)
     received_at: str
 
 
@@ -53,11 +58,21 @@ class CommandEntry(BaseModel):
     responded_at: Optional[str] = None
 
 
+class AlertEventEntry(BaseModel):
+    id: int
+    device_serial: str
+    subsystem: str
+    state: str
+    message: Optional[str] = None
+    occurred_at: str
+
+
 class DeviceMqttStatus(BaseModel):
     device_serial: str
     online: bool
     last_heartbeat: Optional[HeartbeatEntry] = None
     seconds_since_heartbeat: Optional[int] = None
+    last_alert_event: Optional[AlertEventEntry] = None
 
 
 class MqttStatusResponse(BaseModel):
@@ -96,3 +111,99 @@ class DeviceAlertEntry(BaseModel):
 
 class DeviceAlertsResponse(BaseModel):
     alerts: List[DeviceAlertEntry]
+
+
+class AlertEventListResponse(BaseModel):
+    events: List[AlertEventEntry]
+    total: int
+
+
+class BootEventEntry(BaseModel):
+    id: int
+    device_serial: str
+    boot_count: Optional[int] = None
+    reset_reason: Optional[str] = None
+    is_fault: bool = False
+    free_heap: Optional[int] = None
+    crash_task: Optional[str] = None
+    crash_pc: Optional[int] = None
+    crash_exc_cause: Optional[int] = None
+    crash_exc_vaddr: Optional[int] = None
+    occurred_at: str
+
+
+class BootEventListResponse(BaseModel):
+    events: List[BootEventEntry]
+    total: int
+
+
+class PingSampleEntry(BaseModel):
+    id: int
+    device_serial: str
+    rtt_ms: int
+    sampled_at: str
+
+
+class PingSampleListResponse(BaseModel):
+    samples: List[PingSampleEntry]
+    total: int
+
+
+class DiagnosticsReportEntry(BaseModel):
+    id: int
+    device_serial: str
+    cpu_temp_avg: Optional[float] = None
+    cpu_temp_min: Optional[float] = None
+    cpu_temp_max: Optional[float] = None
+    cpu_temp_samples: Optional[int] = None
+    wifi_reconnect_count: Optional[int] = None
+    wifi_last_disconnect_reason: Optional[str] = None
+    wifi_last_disconnect_uptime_ms: Optional[int] = None
+    ota_current_version: Optional[str] = None
+    ota_update_available: Optional[bool] = None
+    ota_available_version: Optional[str] = None
+    ota_last_check_uptime_ms: Optional[int] = None
+    ota_last_error: Optional[str] = None
+    stack_high_water: Optional[str] = None  # JSON-encoded string — see insert_diagnostics_report
+    bell_strikes: Optional[str] = None      # JSON-encoded string, {"0": count, ...} — v2 firmware only
+    bell_loads: Optional[str] = None        # JSON-encoded string, {"0": load, ...} — v2 firmware only
+    cooling_active: Optional[bool] = None   # v2 firmware only
+    received_at: str
+
+
+class DiagnosticsReportListResponse(BaseModel):
+    reports: List[DiagnosticsReportEntry]
+    total: int
+
+
+class DeviceReportEntry(BaseModel):
+    """A control/reports event (currently only bell_overload) — see
+    project-vesper's vesper_mqtt_topic_spec_v2.md. Console-side storage is
+    intentionally light: history/audit only, not a real-time UI surface."""
+    id: int
+    device_serial: str
+    report_type: str
+    payload: Optional[str] = None  # JSON-encoded string
+    occurred_at: str
+
+
+class DeviceReportListResponse(BaseModel):
+    reports: List[DeviceReportEntry]
+    total: int
+
+
+class LatestDiagnosticsEntry(BaseModel):
+    device_serial: str
+    cpu_temp_avg: Optional[float] = None
+    received_at: str
+
+
+class LatestPingEntry(BaseModel):
+    device_serial: str
+    rtt_ms: int
+    sampled_at: str
+
+
+class LatestMetricsResponse(BaseModel):
+    diagnostics: List[LatestDiagnosticsEntry]
+    pings: List[LatestPingEntry]