feat: 新增AI聊天服务，重构任务提示词相关逻辑

1.  新增AI聊天服务接口、实现、控制器及相关DTO、配置类
2.  调整JournalPageTaskTypeEnum枚举值修正
3.  合并任务的基础Prompt和自定义Prompt为单个Prompt字段
4.  精简任务输出DTO冗余属性

QYZH.InteractiveMagazine.WebApi/Controllers/AiChatController.cs

@@ -0,0 +1,50 @@
+using Microsoft.AspNetCore.Mvc;
+using QYZH.InteractiveMagazine.IService;
+using QYZH.InteractiveMagazine.Models.Common;
+using QYZH.InteractiveMagazine.Models.Dto;
+using QYZH.InteractiveMagazine.Models.Enum;
+
+namespace QYZH.InteractiveMagazine.WebApi.Controllers;
+
+/// <summary>
+/// AI聊天控制器
+/// </summary>
+[Route("api/[controller]")]
+[ApiController]
+[ApiExplorerSettings(GroupName = nameof(ApiVersionEnum.Platform))]
+public class AiChatController : BaseController
+{
+    private readonly IAiChatService _aiChatService;
+    private readonly ILogger<AiChatController> _logger;
+
+    public AiChatController(IAiChatService aiChatService, ILogger<AiChatController> logger)
+    {
+        _aiChatService = aiChatService;
+        _logger = logger;
+    }
+
+    /// <summary>
+    /// AI聊天，根据需求生成提示词
+    /// </summary>
+    /// <param name="input">用户需求消息</param>
+    /// <returns>AI生成的提示词（Markdown格式）</returns>
+    [HttpPost]
+    public async Task<BaseResponse<AiChatOutput>> ChatAsync([FromBody] AiChatInput input)
+    {
+        try
+        {
+            var result = await _aiChatService.ChatAsync(input);
+            return Success(result, "AI聊天成功");
+        }
+        catch (BusinessException ex)
+        {
+            _logger.LogWarning(ex, "AI聊天业务异常: {Message}", ex.Message);
+            return BaseResponse<AiChatOutput>.Fail(ex.Message);
+        }
+        catch (Exception ex)
+        {
+            _logger.LogError(ex, "AI聊天系统异常，参数：{Input}", input);
+            return BaseResponse<AiChatOutput>.Fail("AI聊天失败，请稍后重试");
+        }
+    }
+}