Fix backend API parity: document filters, task days param, i18n locales, contract tests

- Add document list filter support (residence, type, category, contractor, is_active, expiring_soon, search) to handler/service/repo
- Add `days` query param parsing to ListTasks handler (matches ListTasksByResidence)
- Add `error.invalid_token` i18n key to all 9 non-English locale files
- Update contract test to include VerificationResponse mapping

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

internal/handlers/task_handler.go

@@ -41,7 +41,19 @@ func (h *TaskHandler) ListTasks(c echo.Context) error {
 		go h.taskService.UpdateUserTimezone(user.ID, tzHeader)
 	}
 
-	response, err := h.taskService.ListTasks(user.ID, userNow)
+	daysThreshold := 30
+	// Support "days" param first, fall back to "days_threshold" for backward compatibility
+	if d := c.QueryParam("days"); d != "" {
+		if parsed, err := strconv.Atoi(d); err == nil {
+			daysThreshold = parsed
+		}
+	} else if d := c.QueryParam("days_threshold"); d != "" {
+		if parsed, err := strconv.Atoi(d); err == nil {
+			daysThreshold = parsed
+		}
+	}
+
+	response, err := h.taskService.ListTasks(user.ID, daysThreshold, userNow)
 	if err != nil {
 		return err
 	}