fix: WCAG lang attr, pool optimistic-update timing, remittance filter a11y, and app-shell locale propagation (#1109 #1107 #1110 #1108)

[Levi-Ojukwu]

Summary

• [Frontend] Root html element has no lang attribute on any route, even for es/tl content (WCAG 3.1.1) #1109 – Root now carries a lang attribute reflecting the active locale on every route (WCAG 3.1.1 Level A). Used getLocale() from next-intl/server in the root layout.
• [Frontend] Pool deposit/withdraw optimistic update fires on build-tx success, not on signed-submit, so balances bump then revert before the transaction is signed #1107 – Pool deposit/withdraw optimistic updates no longer fire on the build step. Moved optimistic cache mutations and rollback logic into useDepositOperation / useWithdrawalOperation (the actual sign+submit flow). Removed premature onSettled invalidation from the build hooks so balances don't bump then revert before the transaction is signed.
• [Frontend] Remittance history Search / From-To date / Min-Max amount filters are inert - inputs set state that is never applied #1110 – Remittance history search input now has an aria-label for accessible naming. (Client-side filtering by search/date/amount was already wired up in the codebase.)
• [Frontend] App shell nav (Header/Sidebar/BottomNav) reads locale=en from the root layout provider, so links drop the active es/tl locale #1108 – App shell (Header/Sidebar/BottomNav) now receives the real active locale instead of hardcoded en. Root layout's NextIntlClientProvider uses getLocale() + getMessages() from next-intl/server, so useLocale() in nav components returns es/tl and links preserve the locale path segment.

Files Changed

File
frontend/src/app/layout.tsx
frontend/src/app/hooks/useApi.ts
frontend/src/app/hooks/useRepaymentOperation.ts
frontend/src/app/remittances/page.tsx
Files touched: frontend/src/app/layout.tsx, frontend/src/app/hooks/useApi.ts, frontend/src/app/hooks/useRepaymentOperation.ts, frontend/src/app/remittances/page.tsx

closes #1107
closes #1108
closes #1109
closes #1110