revert: restore SharePoint download URLs (revert #13)

[devin-ai-integration]

Summary

Reverts the merge of PR #13, which changed dataset download URLs from SharePoint to direct Azure Blob Storage URLs. The blob URLs return 401 errors in browsers because Azure Blob Storage with private access doesn't have a browser-based SSO login flow.

This restores the original SharePoint download links so users can continue downloading datasets while the authenticated Function App download endpoint (#17) is set up and tested.

The URL cutover to the Function App endpoint will be done in a follow-up PR once the full stack is deployed and verified.

Review & Testing Checklist for Human

Low risk — this is a straightforward revert of a single JSON file change.

• Verify the SharePoint download URLs are working after merge (click a dataset download link on the portal)

Notes

• The Azure Blob Storage account and container are still provisioned and ready — this revert only affects the URLs in datasets.json
• Once the Function App is deployed and Easy Auth is configured, a new PR will update the URLs to point to https://bcit-tlu-opendata-dl.azurewebsites.net/api/download?file=<name>.zip

Link to Devin session: https://app.devin.ai/sessions/96d3707e572d4c968d5bfa32f62562e8
Requested by: @kphunter

[devin-ai-integration]

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