Add cache invalidation

JoshHeaps.Net/Services/Implementations/BlogService.cs

@@ -84,5 +84,11 @@ public class BlogService : IBlogService
         return result;
     }
 
+    public void ClearCache()
+    {
+        _cache.Clear();
+        _logger.LogInformation("Blog cache cleared");
+    }
+
     private record CacheEntry(object Value, DateTime ExpiresAt);
 }

JoshHeaps.Net/Services/Interfaces/IBlogService.cs

@@ -7,4 +7,5 @@ public interface IBlogService
     Task<List<BlogPost>> GetAllPostsAsync();
     Task<BlogPost?> GetPostBySlugAsync(string slug);
     Task<List<BlogPost>> GetPostsByTagAsync(string tag);
+    void ClearCache();
 }