Show Home Assistant sensors on the printer card (#1148, #448)

Binds binary_sensor and reading-carrying sensor entities to a printer and
renders their state on its card, worded by Home Assistant's device_class.
Optional per-sensor alert condition drives a notification on the transition
into the alert state and an opt-in interlock that holds queued prints while
alerting -- a hold with a readable waiting_reason, never a failure, and only
ever on a sensor that was read successfully.

Sensors get their own table rather than a wider entity pattern on SmartPlug:
get_smart_plug_by_printer would otherwise hand the card's power button a door
contact to switch.

The hold is passed to the model matcher directly rather than merged into
busy_printers: _check_auto_drying reads that set as "is currently printing"
and would put an idle-but-held printer down the mid-print drying path.

The notification_providers migration spells its default FALSE, not 0 --
Postgres rejects an integer default for a boolean and _safe_execute swallows
the error.

frontend/src/components/NotificationProviderCard.tsx

@@ -144,6 +144,9 @@ export function NotificationProviderCard({ provider, onEdit }: NotificationProvi
             {provider.on_ai_failure_detection && (
               <span className="px-2 py-0.5 bg-fuchsia-100 dark:bg-fuchsia-500/20 text-fuchsia-700 dark:text-fuchsia-300 text-xs rounded">{t('notifications.aiFailureDetection')}</span>
             )}
+            {provider.on_ha_sensor_alert && (
+              <span className="px-2 py-0.5 bg-indigo-100 dark:bg-indigo-500/20 text-indigo-700 dark:text-indigo-300 text-xs rounded">{t('notifications.haSensorAlert')}</span>
+            )}
             {provider.on_filament_low && (
               <span className="px-2 py-0.5 bg-cyan-100 dark:bg-cyan-500/20 text-cyan-700 dark:text-cyan-400 text-xs rounded">{t('notifications.lowFilament')}</span>
             )}
@@ -394,6 +397,17 @@ export function NotificationProviderCard({ provider, onEdit }: NotificationProvi
                   />
                 </div>
 
+                <div className="flex items-center justify-between">
+                  <div>
+                    <p className="text-sm text-white">{t('notifications.haSensorAlert')}</p>
+                    <p className="text-xs text-bambu-gray">{t('notifications.haSensorAlertDescription')}</p>
+                  </div>
+                  <Toggle
+                    checked={provider.on_ha_sensor_alert ?? false}
+                    onChange={(checked) => updateMutation.mutate({ on_ha_sensor_alert: checked })}
+                  />
+                </div>
+
                 <div className="flex items-center justify-between">
                   <p className="text-sm text-white">{t('notifications.lowFilamentLabel')}</p>
 <Toggle