feat(03-01): create 7 core models and 3 service interfaces for Phase 3

- StorageNode, StorageScanOptions models
- SearchResult, SearchOptions models
- DuplicateItem, DuplicateGroup, DuplicateScanOptions models
- IStorageService, ISearchService, IDuplicatesService interfaces

SharepointToolbox/Services/ISearchService.cs

@@ -0,0 +1,13 @@
+using Microsoft.SharePoint.Client;
+using SharepointToolbox.Core.Models;
+
+namespace SharepointToolbox.Services;
+
+public interface ISearchService
+{
+    Task<IReadOnlyList<SearchResult>> SearchFilesAsync(
+        ClientContext ctx,
+        SearchOptions options,
+        IProgress<OperationProgress> progress,
+        CancellationToken ct);
+}