feat(storage): add IFileStorage + local-disk implementation

Adds IFileStorage abstraction and LocalDiskFileStorage for receipt file storage with path-traversal protection, and registers it in DI. Includes 3 TDD-verified xUnit tests.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

API/ROLAC.API/Program.cs

@@ -122,6 +122,8 @@ builder.Services.AddScoped<IGivingCategoryService, GivingCategoryService>();
 builder.Services.AddScoped<IGivingService, GivingService>();
 builder.Services.AddScoped<IOfferingSessionService, OfferingSessionService>();
 builder.Services.AddScoped<IMinistryService, MinistryService>();
+builder.Services.AddScoped<ROLAC.API.Services.Storage.IFileStorage,
+                           ROLAC.API.Services.Storage.LocalDiskFileStorage>();
 
 // ---------------------------------------------------------------------------
 // Swagger / MVC

API/ROLAC.API/Services/Storage/IFileStorage.cs

@@ -0,0 +1,8 @@
+namespace ROLAC.API.Services.Storage;
+
+public interface IFileStorage
+{
+    Task<string> SaveAsync(Stream content, string relativePath, CancellationToken ct = default);
+    Task<Stream?> OpenReadAsync(string relativePath, CancellationToken ct = default);
+    Task DeleteAsync(string relativePath, CancellationToken ct = default);
+}

API/ROLAC.API/Services/Storage/LocalDiskFileStorage.cs

@@ -0,0 +1,53 @@
+using Microsoft.Extensions.Configuration;
+
+namespace ROLAC.API.Services.Storage;
+
+public class LocalDiskFileStorage : IFileStorage
+{
+    private readonly string _root;
+
+    public LocalDiskFileStorage(IConfiguration config)
+    {
+        var configured = config["Storage:LocalRoot"] ?? "App_Data/storage";
+        _root = Path.IsPathRooted(configured)
+            ? configured
+            : Path.Combine(Directory.GetCurrentDirectory(), configured);
+        Directory.CreateDirectory(_root);
+    }
+
+    private string Resolve(string relativePath)
+    {
+        if (string.IsNullOrWhiteSpace(relativePath))
+            throw new ArgumentException("relativePath is required.", nameof(relativePath));
+
+        var normalized = relativePath.Replace('\\', '/').TrimStart('/');
+        var full = Path.GetFullPath(Path.Combine(_root, normalized));
+        var rootFull = Path.GetFullPath(_root) + Path.DirectorySeparatorChar;
+        if (!full.StartsWith(rootFull, StringComparison.Ordinal))
+            throw new ArgumentException("Path escapes storage root.", nameof(relativePath));
+        return full;
+    }
+
+    public async Task<string> SaveAsync(Stream content, string relativePath, CancellationToken ct = default)
+    {
+        var full = Resolve(relativePath);
+        Directory.CreateDirectory(Path.GetDirectoryName(full)!);
+        await using var file = File.Create(full);
+        await content.CopyToAsync(file, ct);
+        return relativePath.Replace('\\', '/').TrimStart('/');
+    }
+
+    public Task<Stream?> OpenReadAsync(string relativePath, CancellationToken ct = default)
+    {
+        var full = Resolve(relativePath);
+        Stream? result = File.Exists(full) ? File.OpenRead(full) : null;
+        return Task.FromResult(result);
+    }
+
+    public Task DeleteAsync(string relativePath, CancellationToken ct = default)
+    {
+        var full = Resolve(relativePath);
+        if (File.Exists(full)) File.Delete(full);
+        return Task.CompletedTask;
+    }
+}

API/ROLAC.API/appsettings.json

@@ -14,5 +14,8 @@
   },
   "Cors": {
     "AllowedOrigins": [ "http://localhost:4200", "https://localhost:4200" ]
+  },
+  "Storage": {
+    "LocalRoot": "App_Data/storage"
   }
 }