Enhance Tender entity with PublicationSubmissionDeadline method and corresponding tests

- Added the PublicationSubmissionDeadline method to the Tender entity, which calculates the submission deadline based on the publication date and stored submission deadline.
- Updated the IsRecommendable method to utilize the new PublicationSubmissionDeadline logic for determining recommendation eligibility.
- Introduced unit tests for the PublicationSubmissionDeadline method, ensuring accurate calculation and validation of submission deadlines.
- Enhanced existing tests for the IsRecommendable method to cover new scenarios related to submission deadlines.

This update improves the accuracy of submission deadline handling and enhances the recommendation logic for tenders based on publication dates.

internal/tender/handler.go

@@ -326,7 +326,7 @@ func (h *TenderHandler) GetPublicTenders(c echo.Context) error {
 
 // RecommendTenders returns AI-ranked tender recommendations for the authenticated customer's company
 // @Summary Get recommended tenders
-// @Description Retrieve AI-ranked tenders with full tender details. AI tender_id values use PROC_{contract_folder_id}/{notice_publication_id}; each item includes rank, analysis, procedure_ref, and the standard tender fields.
+// @Description Retrieve AI-ranked tenders with full tender details. Only active tenders whose publication-based submission window has not passed are returned (submission_deadline, or 48 working hours after publication_date). AI tender_id values use PROC_{contract_folder_id}/{notice_publication_id}; each item includes rank, analysis, procedure_ref, and the standard tender fields.
 // @Tags Tenders
 // @Produce json
 // @Param limit query int false "Number of items per page (default: 10, max: 100)"