feat: 添加用户认证模块

- main.go: 初始化 User/Role 模型、UserRepository、AuthService 和 AuthHandler
- 添加 /auth/register、/auth/login、/auth/me 路由
- auth_handler.go: 新增 GetCurrentUser 接口获取当前用户信息
- .gitignore: 添加 .bitfun/ 目录忽略

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/internal/handler/auth_handler.go

@@ -78,3 +78,27 @@ func (h *AuthHandler) Register(c *gin.Context) {
 		"email":    user.Email,
 	})
 }
+
+// GetCurrentUser 获取当前登录用户信息
+func (h *AuthHandler) GetCurrentUser(c *gin.Context) {
+	userID, exists := c.Get("user_id")
+	if !exists {
+		c.JSON(http.StatusUnauthorized, gin.H{"error": "user not found in context"})
+		return
+	}
+
+	user, err := h.authService.GetUserByID(userID.(string))
+	if err != nil {
+		c.JSON(http.StatusNotFound, gin.H{"error": "user not found"})
+		return
+	}
+
+	c.JSON(http.StatusOK, gin.H{
+		"id":        user.ID,
+		"username":  user.Username,
+		"email":     user.Email,
+		"role_id":   user.RoleID,
+		"is_active": user.IsActive,
+		"created_at": user.CreatedAt,
+	})
+}