[AnVIL DX] Remove azuldownload and curldownload feature flags

[frano-m]

Summary

Remove the azuldownload and curldownload feature flags from the AnVIL Data Explorer so that these features are enabled by default.

Details

The following feature flags are currently gating download functionality:

• AZUL_DOWNLOAD — Controls visibility of the Azul file download column (AzulFileDownload component).
• CURL_DOWNLOAD — Controls visibility of the curl download export method and the /export/get-curl-command route.

These flags are defined in app/shared/entities.ts and referenced in:

• app/components/Index/components/AzulFileDownload/azulFileDownload.tsx
• app/components/Export/components/AnVILExplorer/CurlDownload/curlDownloadExportMethod.tsx
• pages/export/get-curl-command.tsx
• pages/[entityListType]/[...params].tsx

Acceptance criteria

• Remove both feature flag entries from FEATURES enum
• Remove useFeatureFlag checks — features should be unconditionally enabled
• Clean up any related conditional rendering logic
• Verify download column and curl download export method render without feature flags on dev

[MillenniumFalconMechanic]

Completed.