fix(website): pass order property to download dialog field selector

[theosanderson-agent]

Summary

The download dialog's field selector was missing the order property when constructing FieldItem[] arrays from schema metadata. This caused fields and section groups to appear in arbitrary order (based on insertion order) instead of matching the configured order used by both the search form and customize columns modals.

The fix adds order: field.order to the field item mapping in website/src/components/SearchPage/DownloadDialog/FieldSelector/FieldSelectorModal.tsx, ensuring all three field selector modals display metadata in the same consistent order.

Closes #6178

Test plan

• Open the download dialog's field selector and verify sections/fields appear in the same order as the customize columns and search field selectors

🤖 Generated with Claude Code

🚀 Preview: https://fix-download-field-order.loculus.org

[anna-parker]

amazing thanks!

[claude]

Claude finished @anna-parker's task in 36s —— View job

---

Code Review

• Read changed file and common field selector modal
• Analyze fix correctness

The fix is correct and minimal. The common FieldSelectorModal sorts fields within groups by order (line 97 of common/FieldSelectorModal.tsx) and sorts groups by their mean order (line 107). Without order: field.order being passed, all values would be undefined, causing every field to sort to Number.POSITIVE_INFINITY — meaning insertion order was preserved but group ordering was also broken.

The one-line addition resolves both the per-group field ordering and the inter-group header ordering. No other callers of this component are affected since this is the download dialog's own wrapper.

No issues found. LGTM.

[theosanderson]

doesn't matter for this one, but for any slightly bigger PRs we should generally keep to our policy of having two human eyes see it