feat(purchase): 新增主题购买全流程接口

新增主题购买功能，包括余额校验、订单生成、交易记录等完整流程。同时扩展错误码支持余额不足、主题不存在等场景。

src/main/java/com/yolo/keyborad/controller/ThemesController.java

@@ -1,19 +1,20 @@
 package com.yolo.keyborad.controller;
 
+import cn.dev33.satoken.stp.StpUtil;
 import com.yolo.keyborad.common.BaseResponse;
 import com.yolo.keyborad.common.ResultUtils;
+import com.yolo.keyborad.model.dto.purchase.ThemePurchaseReq;
+import com.yolo.keyborad.model.vo.purchase.ThemePurchaseRespVO;
 import com.yolo.keyborad.model.vo.themes.KeyboardThemeStylesRespVO;
 import com.yolo.keyborad.model.vo.themes.KeyboardThemesRespVO;
+import com.yolo.keyborad.service.KeyboardThemePurchaseService;
 import com.yolo.keyborad.service.KeyboardThemeStylesService;
 import com.yolo.keyborad.service.KeyboardThemesService;
 import io.swagger.v3.oas.annotations.Operation;
 import io.swagger.v3.oas.annotations.tags.Tag;
 import jakarta.annotation.Resource;
 import lombok.extern.slf4j.Slf4j;
-import org.springframework.web.bind.annotation.GetMapping;
-import org.springframework.web.bind.annotation.RequestMapping;
-import org.springframework.web.bind.annotation.RequestParam;
-import org.springframework.web.bind.annotation.RestController;
+import org.springframework.web.bind.annotation.*;
 
 import java.util.List;
 
@@ -33,6 +34,9 @@ public class ThemesController {
     @Resource
     private KeyboardThemeStylesService keyboardThemeStylesService;
 
+    @Resource
+    private KeyboardThemePurchaseService themePurchaseService;
+
 
     @GetMapping("/listByStyle")
     @Operation(summary = "按风格查询主题", description = "按主题风格查询主题列表接口")
@@ -46,5 +50,12 @@ public class ThemesController {
         return ResultUtils.success(keyboardThemeStylesService.selectAllThemeStyles());
     }
 
+    @PostMapping("/purchase")
+    @Operation(summary = "购买主题", description = "购买主题接口，扣减用户余额")
+    public BaseResponse<ThemePurchaseRespVO> purchaseTheme(@RequestBody ThemePurchaseReq req) {
+        Long userId = StpUtil.getLoginIdAsLong();
+        ThemePurchaseRespVO result = themePurchaseService.purchaseTheme(userId, req.getThemeId());
+        return ResultUtils.success(result);
+    }
 
 }