feat: page-based navigation shell + Tests page wizard

Replace the monolithic MainWindow with a SelectedPage-driven shell
(Dashboard / Pump / Bench / Tests / Results / Settings). The Tests
page gets the Plan -> Preconditions -> Running -> Done wizard from
ui-structure.md \u00a74, backed by a 7-item precondition gate and
shared sub-views (PhaseCardView / TestSectionView / GraphicIndicatorView)
extracted from the now-deleted monolithic TestPanelView.

New VMs / views:
- Tests wizard: TestPreconditions, PhaseCard, GraphicIndicator,
  TestSection, TestPlan, TestRunning, TestDone
- Dashboard panels: DashboardConnection, DashboardReadings,
  DashboardAlarms, InterlockBanner, ResultHistory
- Pump / bench panels: PumpIdentificationPanel, PumpLiveData,
  UnlockPanel, BenchDriveControl, BenchReadings, RelayBank,
  TemperatureControl, DtcList, AuthGate
- Dialogs: generic ConfirmDialog, UserManageDialog, UserPromptDialog

Supporting changes:
- IsOilPumpOn exposed on MainViewModel for precondition evaluation
- RequiresAuth added to TestDefinition (XML round-trip)
- BipStatusDefinition + CompletedTestRun models
- ~35 new Test.* localization keys (en + es)
- Settings moved from modal dialog to full page
- Pause / Retry / Skip stubs in TestRunningView; full spec in
  docs/gap-test-running-controls.md for follow-up implementation
- docs/ui-structure.md captures the wizard design

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Converters/EnumToIntConverter.cs

@@ -0,0 +1,26 @@
+using System;
+using System.Globalization;
+using System.Windows.Data;
+
+namespace HC_APTBS.Converters
+{
+    /// <summary>
+    /// Two-way converter that maps an enum value to/from its underlying <see cref="int"/> value.
+    ///
+    /// <para>Used to bind <c>TabControl.SelectedIndex</c> (int) to a ViewModel enum property.
+    /// Convert and ConvertBack both honor the actual enum type — pass <c>targetType</c> as the
+    /// enum type when converting back.</para>
+    /// </summary>
+    public sealed class EnumToIntConverter : IValueConverter
+    {
+        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
+            => value is Enum ? System.Convert.ToInt32(value) : 0;
+
+        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
+        {
+            if (value is int i && targetType.IsEnum)
+                return Enum.ToObject(targetType, i);
+            return System.Windows.Data.Binding.DoNothing;
+        }
+    }
+}