Add virtual printer model selection

Features:
  - Configurable printer model for virtual printer emulation
  - Supports X1 series (X1C, X1, X1E), P series (P1S, P1P, P2S),
    A1 series (A1, A1 Mini), and H2 series (H2D, H2C, H2S)
  - Dropdown in Settings > Virtual Printer to select model
  - Model affects SSDP discovery and slicer compatibility
  - Model change restarts virtual printer services automatically

  Backend:
  - Added VIRTUAL_PRINTER_MODELS mapping in manager.py
  - Added virtual_printer_model setting in database
  - New GET /api/v1/settings/virtual-printer/models endpoint
  - Updated PUT /api/v1/settings/virtual-printer to accept model

  Frontend:
  - Added model dropdown to VirtualPrinterSettings component
  - Status display shows selected model name
  - Model change disabled while virtual printer is running

  Tests:
  - Added 3 unit tests for model configuration
  - Updated frontend test mocks for getModels API

backend/tests/unit/services/test_virtual_printer.py

@@ -59,6 +59,54 @@ class TestVirtualPrinterManager:
         with pytest.raises(ValueError, match="Access code is required"):
             await manager.configure(enabled=True)
 
+    @pytest.mark.asyncio
+    async def test_configure_sets_model(self, manager):
+        """Verify configure stores model correctly."""
+        manager._start = AsyncMock()
+
+        await manager.configure(
+            enabled=True,
+            access_code="12345678",
+            mode="immediate",
+            model="C11",  # P1S model code
+        )
+
+        assert manager._model == "C11"
+
+    @pytest.mark.asyncio
+    async def test_configure_ignores_invalid_model(self, manager):
+        """Verify configure ignores invalid model codes."""
+        manager._start = AsyncMock()
+
+        await manager.configure(
+            enabled=True,
+            access_code="12345678",
+            model="INVALID",
+        )
+
+        # Should keep default model
+        assert manager._model == "BL-P001"
+
+    @pytest.mark.asyncio
+    async def test_configure_restarts_on_model_change(self, manager):
+        """Verify model change restarts services when running."""
+        # Simulate running state
+        manager._enabled = True
+        manager._model = "BL-P001"
+        manager._tasks = [MagicMock(done=MagicMock(return_value=False))]
+        manager._stop = AsyncMock()
+        manager._start = AsyncMock()
+
+        await manager.configure(
+            enabled=True,
+            access_code="12345678",
+            model="C11",
+        )
+
+        # Should have stopped and started
+        manager._stop.assert_called_once()
+        manager._start.assert_called_once()
+
     # ========================================================================
     # Tests for status
     # ========================================================================
@@ -67,6 +115,7 @@ class TestVirtualPrinterManager:
         """Verify get_status returns expected fields."""
         manager._enabled = True
         manager._mode = "immediate"
+        manager._model = "C11"
         manager._pending_files = {"file1.3mf": Path("/tmp/file1.3mf")}
         # Simulate running tasks
         manager._tasks = [MagicMock(done=MagicMock(return_value=False))]
@@ -78,6 +127,8 @@ class TestVirtualPrinterManager:
         assert status["mode"] == "immediate"
         assert status["name"] == "Bambuddy"
         assert status["serial"] == "00M09A391800001"
+        assert status["model"] == "C11"
+        assert status["model_name"] == "P1S"
         assert status["pending_files"] == 1
 
     def test_get_status_when_stopped(self, manager):