Enhance API Documentation for Notification Target Audience

- Added "target" field reference to the notification request and response structures in Swagger documentation, improving clarity for API consumers.
- Introduced "notification.TargetAudienceType" definition with enumerated values for target audience options, enhancing the API's usability and understanding.
- Updated related documentation files (YAML and JSON) to reflect these changes, ensuring consistency across all API documentation formats.

internal/assets/handler.go

@@ -47,7 +47,7 @@ func (h *Handler) GetFlagSVG(c echo.Context) error {
 // AdminGetFlag returns a flag by country code (Admin)
 // @Summary Get flag by country code (Admin)
 // @Description Retrieve a country flag by its 3-letter country code for admin panel
-// @Tags Admin Flags
+// @Tags Admin-Flags
 // @Accept json
 // @Produce json
 // @Param country_code path string true "3-letter country code (e.g., POL, GRC)"