feat: improve secret sorting

[rohan-chaturvedi]

Summary

• Add sort menu to the cross-environment secrets editor, matching the existing single-env editor UX
• Persist sort selection in localStorage so it survives page reloads and navigation across both editors
• Make sort menu typography responsive (text-2xs on narrow screens, text-sm on 2xl+) to match input styles

Changes

• frontend/utils/secrets.ts: Add getSavedSort/saveSort helpers for localStorage persistence, and sortAppSecrets for sorting AppSecret[] in the cross-env editor
• frontend/app/[team]/apps/[app]/_components/AppSecrets.tsx: Wire up SortMenu component with localStorage-backed sort state, wrap filtered secrets in useMemo with sort applied
• frontend/app/[team]/apps/[app]/environments/[environment]/[[...path]]/page.tsx: Use getSavedSort/saveSort to persist sort selection
• frontend/components/environments/secrets/SortMenu.tsx: Update typography to text-2xs 2xl:text-sm for responsive sizing

Test plan

• Open single-env editor, change sort order, reload page — sort should persist
• Open cross-env editor — same sort selection should be applied
• Change sort in cross-env editor, navigate to single-env editor — selection should carry over
• On narrow viewport, verify sort menu text matches search input sizing