引入后端API项目并重构前后端桥接与路由

本次提交新增了 Avalonia-API（Web API）与 Avalonia-Services（业务服务）两个项目，完善了解决方案结构。重构了 Avalonia-PC 前端与后端的桥接逻辑，实现了基于前缀的路由分发、静态服务、开发者工具等功能。同步更新了 .gitignore、api.js 及相关配置文件，为后续业务扩展和维护打下基础。

Avalonia-API/Controllers/WeatherForecastController.cs

@@ -0,0 +1,20 @@
+using Avalonia_Services.Models;
+using Avalonia_Services.Services;
+using Microsoft.AspNetCore.Mvc;
+
+namespace Avalonia_API.Controllers
+{
+    [ApiController]
+    [Route("[controller]")]
+    public class WeatherForecastController(WeatherForecastService weatherForecastService) : ControllerBase
+    {
+
+        private readonly WeatherForecastService _weatherForecastService = weatherForecastService;
+
+        [HttpGet(Name = "GetWeatherForecast")]
+        public IEnumerable<WeatherForecast> Get()
+        {
+            return _weatherForecastService.GetWeatherForecasts();
+        }
+    }
+}