Feature/multi printer support (#12)

* Initial implementation of multi-printer support.

* Always show device dropdown and add bambu_diagnose for multi-printer troubleshooting.

* Add multi-AMS support: per-unit snapshot/usage tracking, grouped dashboard panels with real type labels, and dual-nozzle card UX fixes. Fixes a real-world AMS info-code parsing bug found by inspecting live H2C data.

* Add Vortek hotend rack tracking: per-SN registry with slot mapping confirmed against live MQTT capture, plus a fallback for non-inductive nozzles (e.g. H2C's fixed left nozzle) shown read-only without fabricated identity. New dashboard card hides entirely on printers with no Vortek/nozzle-info data at all.

tests/test_resolve_printer_device.py

@@ -0,0 +1,78 @@
+import pytest
+
+from bambu_run.management.commands.bambu_collector import resolve_printer_device
+from bambu_run.models import Printer
+
+
+@pytest.mark.django_db
+def test_creates_new_printer_keyed_by_serial():
+    printer = resolve_printer_device(
+        "0309DA123456", {"name": "RNL-H2C", "dev_product_name": "H2C"}
+    )
+
+    assert printer.serial_number == "0309DA123456"
+    assert printer.name == "RNL-H2C"
+    assert printer.model == "H2C"
+    assert printer.is_active is True
+
+
+@pytest.mark.django_db
+def test_second_call_with_same_serial_does_not_create_duplicate():
+    first = resolve_printer_device("SERIAL-A", {"name": "Printer A", "dev_product_name": "H2C"})
+    second = resolve_printer_device("SERIAL-A", {"name": "Printer A", "dev_product_name": "H2C"})
+
+    assert first.pk == second.pk
+    assert Printer.objects.filter(serial_number="SERIAL-A").count() == 1
+
+
+@pytest.mark.django_db
+def test_two_different_serials_create_two_printers():
+    a = resolve_printer_device("SERIAL-A", {"name": "Printer A", "dev_product_name": "H2C"})
+    b = resolve_printer_device("SERIAL-B", {"name": "Printer B", "dev_product_name": "X1C"})
+
+    assert a.pk != b.pk
+    assert Printer.objects.count() == 2
+
+
+@pytest.mark.django_db
+def test_backfills_single_legacy_printer_with_null_serial():
+    legacy = Printer.objects.create(
+        name="Bambu Lab Printer", model="Bambu Lab", manufacturer="Bambu Lab", is_active=True
+    )
+
+    resolved = resolve_printer_device("SERIAL-A", {"name": "RNL-H2C", "dev_product_name": "H2C"})
+
+    legacy.refresh_from_db()
+    assert resolved.pk == legacy.pk
+    assert legacy.serial_number == "SERIAL-A"
+    assert Printer.objects.count() == 1
+
+
+@pytest.mark.django_db
+def test_does_not_guess_when_multiple_legacy_printers_exist():
+    Printer.objects.create(name="Legacy 1", model="Bambu Lab")
+    Printer.objects.create(name="Legacy 2", model="Bambu Lab")
+
+    resolved = resolve_printer_device("SERIAL-A", {"name": "RNL-H2C", "dev_product_name": "H2C"})
+
+    assert resolved.serial_number == "SERIAL-A"
+    assert Printer.objects.count() == 3
+
+
+@pytest.mark.django_db
+def test_falls_back_to_generic_defaults_without_device_info():
+    printer = resolve_printer_device("SERIAL-A", None)
+
+    assert printer.serial_number == "SERIAL-A"
+    assert printer.name == "Bambu Lab Printer"
+    assert printer.model == "Bambu Lab"
+
+
+@pytest.mark.django_db
+def test_updates_name_and_model_on_existing_printer_when_changed():
+    resolve_printer_device("SERIAL-A", {"name": "Old Name", "dev_product_name": "H2C"})
+
+    updated = resolve_printer_device("SERIAL-A", {"name": "New Name", "dev_product_name": "H2C"})
+
+    assert updated.name == "New Name"
+    assert Printer.objects.filter(serial_number="SERIAL-A").count() == 1