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/Core/Models/SearchOptions.cs

@@ -0,0 +1,15 @@
+namespace SharepointToolbox.Core.Models;
+
+public record SearchOptions(
+    string[] Extensions,
+    string? Regex,
+    DateTime? CreatedAfter,
+    DateTime? CreatedBefore,
+    DateTime? ModifiedAfter,
+    DateTime? ModifiedBefore,
+    string? CreatedBy,
+    string? ModifiedBy,
+    string? Library,
+    int MaxResults,
+    string SiteUrl
+);