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>

Services/IConfigurationService.cs

@@ -79,5 +79,27 @@ namespace HC_APTBS.Services
 
         /// <summary>Replaces all stored user credentials and persists them.</summary>
         void UpdateUsers(Dictionary<string, string> users);
+
+        /// <summary>
+        /// Adds a new user with the given plaintext password.
+        /// Returns false if the username already exists, if either field is empty/whitespace,
+        /// or if the username contains the reserved separator characters <c>':'</c> or <c>','</c>.
+        /// Hashes of existing users are preserved.
+        /// </summary>
+        bool AddUser(string username, string password);
+
+        /// <summary>
+        /// Removes the user with the given username.
+        /// Returns false if the user does not exist or if this would remove the last remaining user.
+        /// Hashes of other users are preserved.
+        /// </summary>
+        bool RemoveUser(string username);
+
+        /// <summary>
+        /// Replaces the stored password for an existing user.
+        /// Returns false if the user does not exist or the password is empty.
+        /// Hashes of other users are preserved.
+        /// </summary>
+        bool ChangeUserPassword(string username, string newPassword);
     }
 }