添加配置管理功能，包括获取和设置配置值的接口及实现

Repository/ConfigRepository.cs

@@ -0,0 +1,19 @@
+namespace Repository;
+
+public interface IConfigRepository : IBaseRepository<ConfigEntity>
+{
+    /// <summary>
+    /// 根据Key获取配置
+    /// </summary>
+    Task<ConfigEntity?> GetByKeyAsync(string key);
+}
+
+public class ConfigRepository(IFreeSql freeSql) : BaseRepository<ConfigEntity>(freeSql), IConfigRepository
+{
+    public async Task<ConfigEntity?> GetByKeyAsync(string key)
+    {
+        return await FreeSql.Select<ConfigEntity>()
+            .Where(c => c.Key == key)
+            .FirstAsync();
+    }
+}