printers: low-toner alerts with configurable thresholds + support-team routing

Poll Zabbix for toner levels on a schedule and email/webhook on a downward
crossing. Warning fires at or below the warning threshold (default 5%),
critical at the critical threshold (default 0%); both thresholds are settings.
State lives in printersupplyalerts so an alert fires once per crossing and
re-arms after a refill.

Recipients mirror the printedparts pattern: plugin-scoped shopdb users +
roles + free-text emails (falling back to the site alert_recipients), and a
chosen support team's webhook (falling back to the site alert_webhook_url).

- PrinterSupplyAlert model + migration printers0002supplyalerts
- alerttier(remaining, warning, critical) + check_supplies poller
- flask printers check-toner-alerts CLI (run via scheduled task/cron)
- printers alert settings + Low-Toner Alerts settings page
- 7 tests: tier boundaries, once-per-crossing + re-arm, toner-only scope,
  custom thresholds, support-team webhook routing

plugins/printers/plugin.py

@@ -9,9 +9,11 @@ from flask import Flask, Blueprint
 import click
 
 from shopdb.plugins.base import BasePlugin, PluginMeta
-from shopdb.api import db, AssetType
+from shopdb.api import db, AssetType, Setting
 
-from .models import Printer, PrinterType, ModelSupply, PrinterDriver
+from .models import (
+    Printer, PrinterType, ModelSupply, PrinterDriver, PrinterSupplyAlert
+)
 from .api import printers_asset_bp
 from .services import ZabbixService
 
@@ -76,6 +78,7 @@ class PrintersPlugin(BasePlugin):
             PrinterType,   # printer type classification
             PrinterDriver, # driver links (SMB/HTTP)
             ModelSupply,   # model -> toner/drum/waste part numbers
+            PrinterSupplyAlert,  # per-printer toner alert crossing state
         ]
 
     def get_services(self) -> Dict[str, Type]:
@@ -103,8 +106,41 @@ class PrintersPlugin(BasePlugin):
         with app.app_context():
             self._ensure_asset_type()
             self._ensure_printer_types()
+            self._seed_settings()
             logger.info("Printers plugin installed")
 
+    def on_enable(self, app: Flask) -> None:
+        # Idempotent re-seed so settings added in later versions reach sites
+        # that installed earlier (enable runs on every upgrade cycle).
+        with app.app_context():
+            self._seed_settings()
+
+    def _seed_settings(self) -> None:
+        """Seed low-toner alert recipient settings (idempotent)."""
+        defaults = [
+            ('printers_alert_email', '', 'string',
+             'Comma-separated low-toner alert recipients; empty uses the '
+             'site alert_recipients'),
+            ('printers_alert_userids', '', 'string',
+             'Comma-separated shopdb user ids whose account emails receive '
+             'low-toner alerts'),
+            ('printers_alert_roleids', '', 'string',
+             'Comma-separated role ids; every active member of these roles '
+             'receives low-toner alerts'),
+            ('printers_alert_supportteamid', '', 'string',
+             'Support team whose webhook receives low-toner alerts; empty '
+             'uses the site alert_webhook_url'),
+            ('printers_alert_warning_threshold', '5', 'integer',
+             'Toner percent remaining at or below which a warning email fires'),
+            ('printers_alert_critical_threshold', '0', 'integer',
+             'Toner percent remaining at or below which a critical email fires'),
+        ]
+        for key, value, valuetype, description in defaults:
+            if Setting.get(key) is None:
+                Setting.set(key, value, valuetype=valuetype,
+                            category='printers', description=description)
+        db.session.commit()
+
     def _ensure_asset_type(self) -> None:
         """Ensure printer asset type exists."""
         existing = AssetType.query.filter_by(assettype='printer').first()
@@ -151,6 +187,19 @@ class PrintersPlugin(BasePlugin):
         """Called when plugin is uninstalled."""
         logger.info("Printers plugin uninstalled")
 
+    def get_settings_cards(self) -> List[dict]:
+        return [
+            {
+                'group': 'Printers',
+                'to': '/settings/printer-alerts',
+                'icon': 'bell',
+                'title': 'Low-Toner Alerts',
+                'description': 'Who gets warning (5%) and critical (0%) toner '
+                               'emails, and which support team webhook',
+                'position': 48,
+            },
+        ]
+
     def get_cli_commands(self) -> List:
         """Return CLI commands for this plugin."""
 
@@ -159,6 +208,22 @@ class PrintersPlugin(BasePlugin):
             """Printers plugin commands."""
             pass
 
+        @printerscli.command('check-toner-alerts')
+        def checktoneralerts():
+            """Poll Zabbix for all printers and email/webhook low-toner crossings.
+
+            Run on a schedule (scheduled task / cron). Fires a warning at or
+            below 5 percent and a critical at 0 percent, once per crossing."""
+            from flask import current_app
+            from .services import check_supplies
+
+            with current_app.app_context():
+                summary = check_supplies()
+                click.echo(
+                    f"Toner poll: {summary['polled']}/{summary['printers']} "
+                    f"printers reachable, {summary['alerts']} alert(s) sent, "
+                    f"{summary['rearmed']} re-armed.")
+
         @printerscli.command('check-supplies')
         @click.argument('ip')
         def checksupplies(ip):