fix: P2 security and correctness issues

P2-10: Change ActivateEmail from GET to POST - token now passed in
request body instead of URL query parameter for better security

P2-11: Change ValidateResetToken from GET to POST - token now passed
in request body instead of URL query parameter to prevent log leakage

P2-12: Note - /uploads static exposure remains (requires architectural
decision about file serving)

P2-13: cursor.Encode() now checks and returns empty string on JSON
marshaling error instead of silently ignoring

P2-14: initDefaultData and ensurePermissions now properly check and
propagate errors from RolePermission creation, and createDefaultPermissions
aggregates errors instead of silently continuing

P2-15: NewJWT now returns (nil, error) on initialization failure
instead of a partially initialized object. All callers updated to handle
the error return.

Backend routes updated:
- POST /auth/activate-email (was GET /activate)
- POST /auth/password/validate (was GET /reset-password)

Frontend updated to match new API endpoints.

internal/api/handler/auth_handler.go

@@ -20,6 +20,11 @@ func newBackgroundCtx(timeoutSec int) (context.Context, context.CancelFunc) {
 	return context.WithTimeout(context.Background(), time.Duration(timeoutSec)*time.Second)
 }
 
+// ActivateEmailRequest 邮箱激活请求
+type ActivateEmailRequest struct {
+	Token string `json:"token" binding:"required"`
+}
+
 // AuthHandler handles authentication requests
 type AuthHandler struct {
 	authService *service.AuthService
@@ -353,19 +358,20 @@ func (h *AuthHandler) GetEnabledOAuthProviders(c *gin.Context) {
 // @Summary 激活用户邮箱
 // @Description 使用邮箱激活token激活用户账号
 // @Tags 邮箱认证
+// @Accept json
 // @Produce json
-// @Param token query string true "激活token"
+// @Param request body ActivateEmailRequest true "激活请求"
 // @Success 200 {object} Response "激活成功"
 // @Failure 400 {object} Response "token缺失"
 // @Failure 401 {object} Response "token无效或已过期"
 // @Router /api/v1/auth/activate-email [post]
 func (h *AuthHandler) ActivateEmail(c *gin.Context) {
-	token := c.Query("token")
-	if token == "" {
+	var req ActivateEmailRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
 		c.JSON(http.StatusBadRequest, gin.H{"code": 400, "message": "token is required"})
 		return
 	}
-	if err := h.authService.ActivateEmail(c.Request.Context(), token); err != nil {
+	if err := h.authService.ActivateEmail(c.Request.Context(), req.Token); err != nil {
 		handleError(c, err)
 		return
 	}