feat: 完善微信授权登录功能

- 新增半屏授权登录窗口，从底部滑出
- 支持微信头像和昵称选择
- 新用户注册默认3个金币
- 新增注销账号功能，从数据库删除用户
- 删除旧的授权登录页面
- 退出登录和注销后跳转首页
- 优化登录交互体验

src/main/java/xuan/controller/UserController.java

@@ -245,4 +245,25 @@ public class UserController {
         }
         return result;
     }
+    
+    @PostMapping("/deleteAccount")
+    public Map<String, Object> deleteAccount(@RequestBody Map<String, Object> params) {
+        Map<String, Object> result = new HashMap<>();
+        try {
+            String userId = params.get("userId").toString();
+            
+            boolean deleted = userInfoService.deleteAccount(userId);
+            if (deleted) {
+                result.put("success", true);
+                result.put("message", "账号已注销");
+            } else {
+                result.put("success", false);
+                result.put("error", "用户不存在");
+            }
+        } catch (Exception e) {
+            result.put("success", false);
+            result.put("error", e.getMessage());
+        }
+        return result;
+    }
 }