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/api/client.ts

@@ -2167,6 +2167,75 @@ export interface HATestConnectionResult {
   error: string | null;
 }
 
+// A Home Assistant entity bound to a printer for display on its card (#1148, #448).
+// Read-only: unlike a SmartPlug there is nothing here to switch.
+export interface PrinterHASensor {
+  id: number;
+  printer_id: number;
+  name: string;
+  entity_id: string;
+  kind: 'binary' | 'numeric';
+  device_class: string | null;  // HA's own class: "door", "temperature", ...
+  unit: string | null;  // numeric sensors only
+  // What counts as needing attention. Binary sensors use alert_state, numeric
+  // ones the thresholds; all null means the sensor is display-only.
+  alert_state: 'on' | 'off' | null;
+  alert_above: number | null;
+  alert_below: number | null;
+  block_print: boolean;  // hold the printer's queue while alerting
+  notify_on_alert: boolean;
+  show_on_printer_card: boolean;
+  sort_order: number;
+  last_state: string | null;
+  last_changed: string | null;
+  last_checked: string | null;
+  created_at: string;
+  updated_at: string;
+}
+
+export interface PrinterHASensorReading {
+  id: number;
+  name: string;
+  entity_id: string;
+  kind: 'binary' | 'numeric';
+  device_class: string | null;
+  unit: string | null;
+  state: string | null;  // null when unreadable or not yet polled
+  value: number | null;  // numeric sensors only
+  alerting: boolean;
+  block_print: boolean;
+  reachable: boolean;
+  last_changed: string | null;
+}
+
+export interface PrinterHASensorCreate {
+  printer_id: number;
+  name: string;
+  entity_id: string;
+  kind: 'binary' | 'numeric';
+  device_class?: string | null;
+  unit?: string | null;
+  alert_state?: 'on' | 'off' | null;
+  alert_above?: number | null;
+  alert_below?: number | null;
+  block_print?: boolean;
+  notify_on_alert?: boolean;
+  show_on_printer_card?: boolean;
+  sort_order?: number;
+}
+
+export type PrinterHASensorUpdate = Partial<Omit<PrinterHASensorCreate, 'printer_id'>>;
+
+// An entity offered by the binding picker.
+export interface HADisplayEntity {
+  entity_id: string;
+  friendly_name: string;
+  state: string | null;
+  domain: string;  // "binary_sensor" | "sensor"
+  device_class: string | null;
+  unit_of_measurement: string | null;
+}
+
 export interface SmartPlugEnergy {
   power: number | null;  // Current watts
   voltage: number | null;  // Volts
@@ -2615,6 +2684,7 @@ export interface NotificationProvider {
   on_plate_clear_required: boolean;
   // Bed cooled
   on_bed_cooled: boolean;
+  on_ha_sensor_alert: boolean;
   // First layer complete
   on_first_layer_complete: boolean;
   // Inventory stock alerts
@@ -2675,6 +2745,7 @@ export interface NotificationProviderCreate {
   on_plate_clear_required?: boolean;
   // Bed cooled
   on_bed_cooled?: boolean;
+  on_ha_sensor_alert?: boolean;
   // First layer complete
   on_first_layer_complete?: boolean;
   // Inventory stock alerts
@@ -2728,6 +2799,7 @@ export interface NotificationProviderUpdate {
   on_plate_clear_required?: boolean;
   // Bed cooled
   on_bed_cooled?: boolean;
+  on_ha_sensor_alert?: boolean;
   // First layer complete
   on_first_layer_complete?: boolean;
   // Inventory stock alerts
@@ -5195,6 +5267,22 @@ export const api = {
   getHASensorEntities: () =>
     request<HASensorEntity[]>('/smart-plugs/ha/sensors'),
 
+  // Home Assistant sensors bound to a printer (#1148, #448)
+  getHASensors: (printerId?: number) =>
+    request<PrinterHASensor[]>(`/ha-sensors/${printerId ? `?printer_id=${printerId}` : ''}`),
+  getHASensorReadings: (printerId: number) =>
+    request<PrinterHASensorReading[]>(`/ha-sensors/by-printer/${printerId}/readings`),
+  getBindableHAEntities: (search?: string) => {
+    const params = search ? `?search=${encodeURIComponent(search)}` : '';
+    return request<HADisplayEntity[]>(`/ha-sensors/entities${params}`);
+  },
+  createHASensor: (data: PrinterHASensorCreate) =>
+    request<PrinterHASensor>('/ha-sensors/', { method: 'POST', body: JSON.stringify(data) }),
+  updateHASensor: (id: number, data: PrinterHASensorUpdate) =>
+    request<PrinterHASensor>(`/ha-sensors/${id}`, { method: 'PATCH', body: JSON.stringify(data) }),
+  deleteHASensor: (id: number) =>
+    request<{ message: string }>(`/ha-sensors/${id}`, { method: 'DELETE' }),
+
   // REST smart plug
   testRESTConnection: (url: string, method: string = 'GET', headers?: string | null) =>
     request<{ success: boolean; error: string | null }>('/smart-plugs/rest/test-connection', {