Update the multi-dataset download feature so users can download cluster-only dataset

[howardwkim]

Summary

Update the multi-dataset download feature so users can download cluster-only datasets

What This Includes

• Backend changes to support cluster-only datasets in multi-dataset download
• Same CSV output format as existing downloads (no change to user experience)
• Same download workflow from user perspective (select datasets → download ZIP)
• Verification with known cluster-only dataset

What This Does NOT Include

• Shared utility refactoring is not included - The fix will be implemented directly in the bulk download code. Creating a reusable cluster module for other parts of the system is a separate effort.

• Changes to single-dataset download are not included

• User interface changes are not included - The download interface remains the same. Users will not see any difference in how they initiate downloads. No changes to cmap-react codebase.

Assumptions

• I'm assuming the priority is fixing the functionality, not optimizing performance

[mdashkezari]

This issue should only address the cluster-only downloads within the Collection feature which means:

• User must be able to download cluster-only datasets the same as other datasets
• The returned CSV/Excel files must have the same structure, formatting
• Double check if time formatting is consistent with non-cluster CSVs
• No special UI-treatment is needed for cluster-only datasets
• Backend changes to support cluster-only datasets in multi-dataset download
• Once ready, test if download from these tables work correctly:

tblAltimetry_NRT_Signal
tblModis_PAR_NRT
tblPisces_Forecast_Co2
tblPisces_Forecast_Nutrients
tblPisces_Forecast_cl1

Shared utility refactoring is not included - The fix will be implemented directly in the bulk download code. Creating a reusable cluster module for other parts of the system is a separate effort.

Changes to single-dataset download are not included

[howardwkim]

lgtm

[mdashkezari]

Now we both agree on this ticket and its extent. Delivery date estimated by Howard 2026-01-02