feat(07-01): add IUserAccessAuditService and IGraphUserSearchService interfaces

- IUserAccessAuditService.AuditUsersAsync: scan sites and filter by user logins
- IGraphUserSearchService.SearchUsersAsync: Graph API people-picker autocomplete
- GraphUserResult record: DisplayName, UserPrincipalName, Mail

SharepointToolbox/Services/IUserAccessAuditService.cs

@@ -0,0 +1,30 @@
+using SharepointToolbox.Core.Models;
+
+namespace SharepointToolbox.Services;
+
+/// <summary>
+/// Scans permissions across selected sites and filters results to show
+/// only what specific user(s) can access.
+/// </summary>
+public interface IUserAccessAuditService
+{
+    /// <summary>
+    /// Scans all selected sites for permissions, then filters results to entries
+    /// matching the specified user logins. Returns a flat list of UserAccessEntry
+    /// records suitable for DataGrid binding and export.
+    /// </summary>
+    /// <param name="sessionManager">Session manager for creating authenticated contexts.</param>
+    /// <param name="targetUserLogins">Login names (emails) of users to audit.</param>
+    /// <param name="sites">Sites to scan.</param>
+    /// <param name="options">Scan depth options (inherited, folders, subsites).</param>
+    /// <param name="progress">Progress reporter.</param>
+    /// <param name="ct">Cancellation token.</param>
+    /// <returns>Flat list of access entries for the target users.</returns>
+    Task<IReadOnlyList<UserAccessEntry>> AuditUsersAsync(
+        ISessionManager sessionManager,
+        IReadOnlyList<string> targetUserLogins,
+        IReadOnlyList<SiteInfo> sites,
+        ScanOptions options,
+        IProgress<OperationProgress> progress,
+        CancellationToken ct);
+}