test(02-01): scaffold PermissionsService, ViewModel, and classification test stubs

- PermissionEntryHelper.cs: pure static IsExternalUser, FilterPermissionLevels, IsSharingLinksGroup
- PermissionEntryClassificationTests.cs: 7 real [Fact] tests — all passing immediately
- PermissionsServiceTests.cs: 2 stubs (PERM-01, PERM-04) skipped until Plan 02 CSOM impl
- PermissionsViewModelTests.cs: 1 stub (PERM-02) skipped until Plan 02 ViewModel impl

SharepointToolbox.Tests/Services/PermissionsServiceTests.cs

@@ -0,0 +1,31 @@
+using SharepointToolbox.Core.Models;
+using SharepointToolbox.Services;
+
+namespace SharepointToolbox.Tests.Services;
+
+/// <summary>
+/// Test stubs for PERM-01 and PERM-04.
+/// These tests are skipped until IPermissionsService is implemented in Plan 02.
+/// </summary>
+public class PermissionsServiceTests
+{
+    [Fact(Skip = "Requires live CSOM context — covered by Plan 02 implementation")]
+    public async Task ScanSiteAsync_ReturnsPermissionEntries_ForMockedSite()
+    {
+        // PERM-01: ScanSiteAsync returns a list of PermissionEntry records
+        // Arrange — requires a real or mocked ClientContext (CSOM)
+        // Act
+        // Assert
+        await Task.CompletedTask;
+    }
+
+    [Fact(Skip = "Requires live CSOM context — covered by Plan 02 implementation")]
+    public async Task ScanSiteAsync_WithIncludeInheritedFalse_SkipsItemsWithoutUniquePermissions()
+    {
+        // PERM-04: When IncludeInherited = false, items without unique permissions are excluded
+        // Arrange — requires a real or mocked ClientContext (CSOM)
+        // Act
+        // Assert
+        await Task.CompletedTask;
+    }
+}